For #10494: Process HomeMenu builder changes on the main thread

Problem was that we were trying to process menu changes (in response to account manager events) on some background thread as that's what account manager emits them on, so some code internally in PopupWindow's dismiss handling (i think, didn't dig very deeply here) was silently giving up and we'd get into a bad state.

The reason this seemingly only happened if you quickly opened a menu on startup is because account manager isn't initialized until sometime after the startup finished. So the trick was to open the menu (and register account manager state callbacks) before it got initialized, so that the callbacks are invoked.

This should also reproduce in other, much more obscure ways, e.g. if you open the menu right before sync is scheduled to run in the background, change FxA password on another connected client, and then eventually receive a onAuthenticationProblem callback.

app/src/main/java/org/mozilla/fenix/home/HomeMenu.kt

@@ -8,6 +8,9 @@ import android.content.Context
 import androidx.core.content.ContextCompat.getColor
 import androidx.lifecycle.Lifecycle
 import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.lifecycleScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
 import mozilla.components.browser.menu.BrowserMenuBuilder
 import mozilla.components.browser.menu.BrowserMenuHighlight
 import mozilla.components.browser.menu.ext.getHighlight
@@ -174,21 +177,31 @@ class HomeMenu(
             }
             context.components.backgroundServices.accountManager.register(object : AccountObserver {
                 override fun onAuthenticationProblems() {
-                    onMenuBuilderChanged(BrowserMenuBuilder(
-                        listOf(reconnectToSyncItem) + coreMenuItems
-                    ))
+                    lifecycleOwner.lifecycleScope.launch(Dispatchers.Main) {
+                        onMenuBuilderChanged(BrowserMenuBuilder(
+                            listOf(reconnectToSyncItem) + coreMenuItems
+                        ))
+                    }
                 }
 
                 override fun onAuthenticated(account: OAuthAccount, authType: AuthType) {
-                    onMenuBuilderChanged(BrowserMenuBuilder(
-                        coreMenuItems
-                    ))
+                    lifecycleOwner.lifecycleScope.launch(Dispatchers.Main) {
+                        onMenuBuilderChanged(
+                            BrowserMenuBuilder(
+                                coreMenuItems
+                            )
+                        )
+                    }
                 }
 
                 override fun onLoggedOut() {
-                    onMenuBuilderChanged(BrowserMenuBuilder(
-                        coreMenuItems
-                    ))
+                    lifecycleOwner.lifecycleScope.launch(Dispatchers.Main) {
+                        onMenuBuilderChanged(
+                            BrowserMenuBuilder(
+                                coreMenuItems
+                            )
+                        )
+                    }
                 }
             }, lifecycleOwner)
         }