Provide a preference to scale all UI text (#3248)

Font scaling is applied in addition to any scaling set in Android system preferences. So if the user set the Android font size to largest (a 1.3x increase) and then sets the preference to 120%, the total change is 1.56x.

Create SliderPreference to adjust the preference.

- Use Slider, which supports float values and step sizes > 1
- Display the selected value in the preference's summary
- Provide buttons to increment / decrement the value

Restart the activity if the preference changes so that the user sees the impact of the change immediately. Fix a bug in PreferencesActivity where the "EXTRA_RESTART_ON_BACK" intent was never processed. Fix this to ensure that other activities are restarted so the new font scale takes effect.

Implement the scaling in BaseActivity by overriding onAttachBaseContext, and providing a wrapped context with the font scaling applied.

Fixes https://github.com/tuskyapp/Tusky/issues/2982, https://github.com/tuskyapp/Tusky/issues/2461

app/src/main/java/com/keylesspalace/tusky/view/SliderPreference.kt

@@ -0,0 +1,185 @@
+package com.keylesspalace.tusky.view
+
+import android.content.Context
+import android.content.res.TypedArray
+import android.graphics.drawable.Drawable
+import android.util.AttributeSet
+import android.view.View.VISIBLE
+import androidx.appcompat.content.res.AppCompatResources
+import androidx.preference.Preference
+import androidx.preference.PreferenceViewHolder
+import com.google.android.material.slider.LabelFormatter.LABEL_GONE
+import com.google.android.material.slider.Slider
+import com.keylesspalace.tusky.R
+import com.keylesspalace.tusky.databinding.PrefSliderBinding
+import java.lang.Float.max
+import java.lang.Float.min
+
+/**
+ * Slider preference
+ *
+ * Similar to [androidx.preference.SeekBarPreference], but better because:
+ *
+ * - Uses a [Slider] instead of a [android.widget.SeekBar]. Slider supports float values, and step sizes
+ *   other than 1.
+ * - Displays the currently selected value in the Preference's summary, for consistency
+ *   with platform norms.
+ * - Icon buttons can be displayed at the start/end of the slider. Pressing them will
+ *   increment/decrement the slider by `stepSize`.
+ * - User can supply a custom formatter to format the summary value
+ */
+class SliderPreference @JvmOverloads constructor(
+    context: Context,
+    attrs: AttributeSet? = null,
+    defStyleAttr: Int = androidx.preference.R.attr.preferenceStyle,
+    defStyleRes: Int = 0
+) : Preference(context, attrs, defStyleAttr, defStyleRes),
+    Slider.OnChangeListener,
+    Slider.OnSliderTouchListener {
+
+    /** Backing property for `value` */
+    private var _value = 0F
+
+    /**
+     * @see Slider.getValue
+     * @see Slider.setValue
+     */
+    var value: Float = defaultValue
+        get() = _value
+        set(v) {
+            val clamped = max(max(v, valueFrom), min(v, valueTo))
+            if (clamped == field) return
+            _value = clamped
+            persistFloat(v)
+            notifyChanged()
+        }
+
+    /** @see Slider.setValueFrom */
+    var valueFrom: Float
+
+    /** @see Slider.setValueTo */
+    var valueTo: Float
+
+    /** @see Slider.setStepSize */
+    var stepSize: Float
+
+    /**
+     * Format string to be applied to values before setting the summary. For more control set
+     * [SliderPreference.formatter]
+     */
+    var format: String = defaultFormat
+
+    /**
+     * Function that will be used to format the summary. The default formatter formats using the
+     * value of the [SliderPreference.format] property.
+     */
+    var formatter: (Float) -> String = { format.format(it) }
+
+    /**
+     * Optional icon to show in a button at the start of the slide. If non-null the button is
+     * shown. Clicking the button decrements the value by one step.
+     */
+    var decrementIcon: Drawable? = null
+
+    /**
+     * Optional icon to show in a button at the end of the slider. If non-null the button is
+     * shown. Clicking the button increments the value by one step.
+     */
+    var incrementIcon: Drawable? = null
+
+    /** View binding */
+    private lateinit var binding: PrefSliderBinding
+
+    init {
+        // Using `widgetLayoutResource` here would be incorrect, as that tries to put the entire
+        // preference layout to the right of the title and summary.
+        layoutResource = R.layout.pref_slider
+
+        val a = context.obtainStyledAttributes(attrs, R.styleable.SliderPreference, defStyleAttr, defStyleRes)
+
+        value = a.getFloat(R.styleable.SliderPreference_android_value, defaultValue)
+        valueFrom = a.getFloat(R.styleable.SliderPreference_android_valueFrom, defaultValueFrom)
+        valueTo = a.getFloat(R.styleable.SliderPreference_android_valueTo, defaultValueTo)
+        stepSize = a.getFloat(R.styleable.SliderPreference_android_stepSize, defaultStepSize)
+        format = a.getString(R.styleable.SliderPreference_format) ?: defaultFormat
+
+        val decrementIconResource = a.getResourceId(R.styleable.SliderPreference_iconStart, -1)
+        if (decrementIconResource != -1) {
+            decrementIcon = AppCompatResources.getDrawable(context, decrementIconResource)
+        }
+
+        val incrementIconResource = a.getResourceId(R.styleable.SliderPreference_iconEnd, -1)
+        if (incrementIconResource != -1) {
+            incrementIcon = AppCompatResources.getDrawable(context, incrementIconResource)
+        }
+
+        a.recycle()
+    }
+
+    override fun onGetDefaultValue(a: TypedArray, i: Int): Any {
+        return a.getFloat(i, defaultValue)
+    }
+
+    override fun onSetInitialValue(defaultValue: Any?) {
+        value = getPersistedFloat((defaultValue ?: Companion.defaultValue) as Float)
+    }
+
+    override fun onBindViewHolder(holder: PreferenceViewHolder) {
+        super.onBindViewHolder(holder)
+        binding = PrefSliderBinding.bind(holder.itemView)
+
+        binding.root.isClickable = false
+
+        binding.slider.addOnChangeListener(this)
+        binding.slider.addOnSliderTouchListener(this)
+        binding.slider.value = value // sliderValue
+        binding.slider.valueTo = valueTo
+        binding.slider.valueFrom = valueFrom
+        binding.slider.stepSize = stepSize
+
+        // Disable the label, the value is shown in the preference summary
+        binding.slider.labelBehavior = LABEL_GONE
+        binding.slider.isEnabled = isEnabled
+
+        binding.summary.visibility = VISIBLE
+        binding.summary.text = formatter(value)
+
+        decrementIcon?.let { icon ->
+            binding.decrement.icon = icon
+            binding.decrement.visibility = VISIBLE
+            binding.decrement.setOnClickListener {
+                value -= stepSize
+            }
+        }
+
+        incrementIcon?.let { icon ->
+            binding.increment.icon = icon
+            binding.increment.visibility = VISIBLE
+            binding.increment.setOnClickListener {
+                value += stepSize
+            }
+        }
+    }
+
+    override fun onValueChange(slider: Slider, value: Float, fromUser: Boolean) {
+        if (!fromUser) return
+        binding.summary.text = formatter(value)
+    }
+
+    override fun onStartTrackingTouch(slider: Slider) {
+        // Deliberately empty
+    }
+
+    override fun onStopTrackingTouch(slider: Slider) {
+        value = slider.value
+    }
+
+    companion object {
+        private const val TAG = "SliderPreference"
+        private const val defaultValueFrom = 0F
+        private const val defaultValueTo = 1F
+        private const val defaultValue = 0.5F
+        private const val defaultStepSize = 0.1F
+        private const val defaultFormat = "%3.1f"
+    }
+}