Prevent parallel loading and fix duplicate ViewModel state collection in FiltersActivity (#4472)

This pull request fixes the following issues:

- `FiltersActivity` launches a new coroutine to collect the ViewModel
state every time the Activity is resumed, without cancelling the
previous coroutine.
- `FiltersActivity` reloads the filters in `onResume()`, even if loading
is already in progress (without cancelling the current loading). This
can lead to inconsistent state.

List of improvements:
- Implement `launchAndRepeatOnLifecycle()` to combine
`coroutineScope.launch()` with `repeatOnLifecycle()` for the same
`Lifecycle`. Use it in `FiltersActivity` to update the view only when
the Activity is visible.
- Optimize the filters loading: load them when `FiltersViewModel` is
created and when returning from `EditFilterActivity` (when receiving the
Activity result). Cancel the load already in progress, if any.
- use `MutableStateFlow.update()` to update the state in a thread-safe
way.
- Turn `FiltersViewModel.deleteFilter()` into a suspending function in
order to perform the update in the coroutinescope of the Activity
lifecycle, so the View passed as argument doesn't leak.
- Wait for an ongoing load operation to complete before performing a
delete filter operation, so the state stays consistent.
- Add `Intent.withSlideInAnimation()` as a simpler and more flexible
alternative to `Activity.startActivityWithSlideInAnimation(Intent)`.

app/src/main/java/com/keylesspalace/tusky/util/ActivityExtensions.kt

@@ -12,10 +12,13 @@ import androidx.lifecycle.LifecycleEventObserver
 import com.keylesspalace.tusky.BaseActivity
 
 fun Activity.startActivityWithSlideInAnimation(intent: Intent) {
+    startActivity(intent.withSlideInAnimation())
+}
+
+fun Intent.withSlideInAnimation(): Intent {
     // the new transition api needs to be called by the activity that is the result of the transition,
     // so we pass a flag that BaseActivity will respect.
-    intent.putExtra(BaseActivity.OPEN_WITH_SLIDE_IN, true)
-    startActivity(intent)
+    return putExtra(BaseActivity.OPEN_WITH_SLIDE_IN, true)
 }
 
 /**

app/src/main/java/com/keylesspalace/tusky/util/LifecycleExtensions.kt

@@ -0,0 +1,21 @@
+package com.keylesspalace.tusky.util
+
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.coroutineScope
+import androidx.lifecycle.repeatOnLifecycle
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.launch
+
+fun Lifecycle.launchAndRepeatOnLifecycle(
+    state: Lifecycle.State = Lifecycle.State.STARTED,
+    block: suspend CoroutineScope.() -> Unit
+): Job = coroutineScope.launch {
+    repeatOnLifecycle(state, block)
+}
+
+fun LifecycleOwner.launchAndRepeatOnLifecycle(
+    state: Lifecycle.State = Lifecycle.State.STARTED,
+    block: suspend CoroutineScope.() -> Unit
+): Job = lifecycle.launchAndRepeatOnLifecycle(state, block)