Add a config to control split-screen task dimming

In split-screen when a task is the IME target, the other one is dimmed.
Add a config to enable/disable this functionality.

Test: Manual
Bug: 229090560
Change-Id: Id0935f1badec4620a97b8ea9826d32b94c186b98
Merged-In: If41d89744acd6dcba27085755b6cd3947ee3ad62
2 files changed