Invalidate home task snapshot onWakeAndUnlock.

Also, add ability to pass in null to invalidateHomeTaskSnapshot
if the correct permissions are held, so that System UI does not
need to IPC to Launcher to ask it to invalidate itself.

Fixes: 229191103
Test: atest SystemUITests
Test: wake and unlock, note no double launcher
Change-Id: I0c547639979460b3a85b0ef0a8bbf760d60054cb