Visual stability for modes dialog

If a tile should disappear after being pressed, keep it in the grid
while the dialog is visible.

Bug: 346519570
Test: ModesDialogViewModelTest + manually tested with bedtime mode, which currently doesn't support manual invocation
Flag: android.app.modes_ui
Change-Id: I7658ddd52d7f349829a991a1b414efc7158cc03e