Use concurrent list to prevent ConcurrentModificationException

TasksRepository.setVisibleTasks can add/remove listeners while HighResLoadingState.updateState iterates over them.

Bug: 408978565
Flag: com.android.launcher3.enable_refactor_task_thumbnail
Test: SwitchBackToSplitFromRecentGesturalNavLandscape#switchBackToSplitFromRecent
Test: Manual - made exception extremely likely by constantly adding/removing listeners. Could easily repro exceptions, then added this CL and could no longer repro.
Change-Id: Ic04717527fcbdb9301a6e313f9e666e2f5135b3e

quickstep/src/com/android/quickstep/HighResLoadingState.kt

@@ -18,6 +18,7 @@ package com.android.quickstep
 
 import android.content.res.Resources
 import com.android.quickstep.recents.data.HighResLoadingStateNotifier
+import java.util.concurrent.CopyOnWriteArrayList
 
 /** Determines when high res or low res thumbnails should be loaded. */
 class HighResLoadingState : HighResLoadingStateNotifier {
@@ -38,7 +39,7 @@ class HighResLoadingState : HighResLoadingStateNotifier {
     var isEnabled: Boolean = false
         private set
 
-    private val callbacks = ArrayList<HighResLoadingStateChangedCallback>()
+    private val callbacks = CopyOnWriteArrayList<HighResLoadingStateChangedCallback>()
 
     interface HighResLoadingStateChangedCallback {
         fun onHighResLoadingStateChanged(enabled: Boolean)
@@ -56,7 +57,7 @@ class HighResLoadingState : HighResLoadingStateNotifier {
         val prevState = isEnabled
         isEnabled = forceHighResThumbnails || (visible && !flingingFast)
         if (prevState != isEnabled) {
-            for (callback in callbacks.asReversed()) {
+            for (callback in callbacks) {
                 callback.onHighResLoadingStateChanged(isEnabled)
             }
         }