gd/gc: Ensure GD UIs displayed above GC input mapping

This CL ensures that the GD UIs including the welcome dialog and main
menu are displayed above GC input mapping when GC input mapping shows
up.

Bug: b/328124321
Test: manually test
Change-Id: I8e30c479776cf430fbf6e0be0a7d37fba9b694fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5342602


Reviewed-by: Prameet Shah <phshah@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Cici Ruan <cuicuiruan@google.com>
Cr-Commit-Position: refs/heads/main@{#1270491}