inject SharedPreferences (#4441)

(this one is for @charlag)

Calling `PreferenceManager.getDefaultSharedPreferences()` will read the
preference file from disk every time. This PR makes `SharedPreferences`
a singleton so they will only be created once at appstart (with a few
exceptions where it is hard to inject, e.g. in the `openLink` helper)
which should help getting our ANRs down.

```
StrictMode policy violation; ~duration=285 ms: android.os.strictmode.DiskReadViolation
    at android.os.StrictMode$AndroidBlockGuardPolicy.onReadFromDisk(StrictMode.java:1666)
    at libcore.io.BlockGuardOs.access(BlockGuardOs.java:74)
    at libcore.io.ForwardingOs.access(ForwardingOs.java:128)
    at android.app.ActivityThread$AndroidOs.access(ActivityThread.java:8054)
    at java.io.UnixFileSystem.checkAccess(UnixFileSystem.java:313)
    at java.io.File.exists(File.java:813)
    at android.app.ContextImpl.ensurePrivateDirExists(ContextImpl.java:790)
    at android.app.ContextImpl.ensurePrivateDirExists(ContextImpl.java:781)
    at android.app.ContextImpl.getPreferencesDir(ContextImpl.java:737)
    at android.app.ContextImpl.getSharedPreferencesPath(ContextImpl.java:962)
    at android.app.ContextImpl.getSharedPreferences(ContextImpl.java:583)
    at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:221)
    at android.content.ContextWrapper.getSharedPreferences(ContextWrapper.java:221)
    at androidx.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:119)
    at com.keylesspalace.tusky.BaseActivity.onCreate(BaseActivity.java:96)
   ...
```

app/src/test/java/com/keylesspalace/tusky/MainActivityTest.kt

@@ -140,6 +140,13 @@ class MainActivityTest {
             onBlocking { accountVerifyCredentials() } doReturn NetworkResult.success(account)
             onBlocking { listAnnouncements(false) } doReturn NetworkResult.success(emptyList())
         }
+        activity.preferences = mock(defaultAnswer = {
+            when (it.method.returnType) {
+                String::class.java -> "test"
+                Boolean::class.java -> false
+                else -> null
+            }
+        })
         controller.create().start()
         return activity
     }

app/src/test/java/com/keylesspalace/tusky/TuskyApplication.kt

@@ -16,14 +16,20 @@
 package com.keylesspalace.tusky
 
 import android.app.Application
+import android.content.SharedPreferences
+import com.keylesspalace.tusky.di.PreferencesEntryPoint
+import dagger.hilt.internal.GeneratedComponent
 import de.c1710.filemojicompat_defaults.DefaultEmojiPackList
 import de.c1710.filemojicompat_ui.helpers.EmojiPackHelper
+import org.mockito.kotlin.mock
 
 // override TuskyApplication for Robolectric tests, only initialize the necessary stuff
-class TuskyApplication : Application() {
+class TuskyApplication : Application(), PreferencesEntryPoint, GeneratedComponent {
 
     override fun onCreate() {
         super.onCreate()
         EmojiPackHelper.init(this, DefaultEmojiPackList.get(this))
     }
+
+    override fun preferences(): SharedPreferences = mock {}
 }

app/src/test/java/com/keylesspalace/tusky/components/compose/ComposeActivityTest.kt

@@ -163,6 +163,14 @@ class ComposeActivityTest {
         activity.accountManager = accountManagerMock
         activity.viewModelProviderFactory = testViewModelFactory
 
+        activity.preferences = mock(defaultAnswer = {
+            when (it.method.returnType) {
+                String::class.java -> "test"
+                Boolean::class.java -> false
+                else -> null
+            }
+        })
+
         controller.create().start()
         shadowOf(getMainLooper()).idle()
     }