Hide system UI until the shared element transition completes.

app/src/main/java/org/thoughtcrime/securesms/mediapreview/MediaPreviewV2Fragment.kt

@@ -185,6 +185,15 @@ class MediaPreviewV2Fragment : LoggingFragment(R.layout.fragment_media_preview_v
   private fun initializeFullScreenUi() {
     fullscreenHelper.configureToolbarLayout(binding.toolbarCutoutSpacer, binding.toolbar)
     fullscreenHelper.showAndHideWithSystemUI(requireActivity().window, binding.toolbarLayout, binding.mediaPreviewDetailsContainer)
+    fullscreenHelper.hideSystemUI()
+
+    lifecycleDisposable += viewModel.state.map {
+      it.isInSharedAnimation to it.loadState
+    }.distinctUntilChanged().subscribe { (isInSharedAnimation, loadState) ->
+      if (!isInSharedAnimation && loadState == MediaPreviewV2State.LoadState.MEDIA_READY) {
+        fullscreenHelper.showSystemUI()
+      }
+    }
   }
 
   private fun bindCurrentState(currentState: MediaPreviewV2State) {