StrictMode ThreadPolicy violation calling WallpaperFileManager.clean

[Amejia481]

This is only happening on debug builds

  FATAL EXCEPTION: pool-6-thread-2
Process: org.mozilla.fenix.debug, PID: 9766
java.lang.RuntimeException: StrictMode ThreadPolicy violation
	at org.mozilla.fenix.perf.ThreadPenaltyDeathWithIgnoresListener.penaltyDeath(ThreadPenaltyDeathWithIgnoresListener.kt:45)
	at org.mozilla.fenix.perf.ThreadPenaltyDeathWithIgnoresListener.onThreadViolation(ThreadPenaltyDeathWithIgnoresListener.kt:39)
	at android.os.StrictMode$AndroidBlockGuardPolicy.lambda$onThreadPolicyViolation$1(StrictMode.java:1719)
	at android.os.-$$Lambda$StrictMode$AndroidBlockGuardPolicy$FxZGA9KtfTewqdcxlUwvIe5Nx9I.run(Unknown Source:4)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.lang.Thread.run(Thread.java:764)
Caused by: android.os.strictmode.DiskReadViolation
	at android.os.StrictMode$AndroidBlockGuardPolicy.onReadFromDisk(StrictMode.java:1504)
	at java.io.UnixFileSystem.getBooleanAttributes(UnixFileSystem.java:241)
	at java.io.File.isDirectory(File.java:845)
	at kotlin.io.FileTreeWalk$FileTreeWalkIterator.<init>(FileTreeWalk.kt:73)
	at kotlin.io.FileTreeWalk.iterator(FileTreeWalk.kt:50)
	at org.mozilla.fenix.wallpapers.WallpaperFileManager.cleanChildren(WallpaperFileManager.kt:49)
	at org.mozilla.fenix.wallpapers.WallpaperFileManager.clean(WallpaperFileManager.kt:44)
	at org.mozilla.fenix.wallpapers.WallpaperManager.<init>(WallpaperManager.kt:50)
	at org.mozilla.fenix.wallpapers.WallpaperManager.<init>(WallpaperManager.kt:32)
	at org.mozilla.fenix.components.Components$wallpaperManager$2.invoke(Components.kt:148)
	at org.mozilla.fenix.components.Components$wallpaperManager$2.invoke(Components.kt:147)
	at kotlin.SynchronizedLazyImpl.getValue(LazyJVM.kt:74)
	at org.mozilla.fenix.components.Components.getWallpaperManager(Components.kt:147)
	at org.mozilla.fenix.home.HomeFragment.displayWallpaperIfEnabled(HomeFragment.kt:1238)
	at org.mozilla.fenix.home.HomeFragment.onCreateView(HomeFragment.kt:407)
	at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2963)
	at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:518)
	at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
	at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
	at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2106)
	at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002)
	at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3138)
	at androidx.fragment.app.FragmentManager.dispatchViewCreated(FragmentManager.java:3065)
	at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2988)
	at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:546)
	at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282)
	at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
	at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647)
	at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128)
	at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:3072)
	at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:251)
	at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:501)
	at androidx.appcompat.app.AppCompatActivity.onStart(AppCompatActivity.java:246)
	at org.mozilla.fenix.HomeActivity.onStart(HomeActivity.kt:360)
	at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1391)
	at androidx.test.runner.MonitoringInstrumentation.callActivityOnStart(MonitoringInstrumentation.java:723)
	at android.app.Activity.performStart(Activity.java:7157)
	at android.app.ActivityThread.handleStartActivity(ActivityThread.java:2937)

┆Issue is synchronized with this Jira Task