Restrict activity launch when caller is running in the background

Cherry picked Ie3bc5bd88bfd3bd4777210c0740ad34ea6d3311e to master due to b/286408867.

Code was merged via `-s ours` and is missing even though the sha exists on the target branch. Cherry pick is required to bring in the code.

Manually remove the "Merged in" directive to allow for downstream propagation.

Test: atest BackgroundActivityLaunchTest#testBackgroundActivityBlockedInStartNextMatchingActivity
Bug: 230492947
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:e3c537ddea5ce8b28eeb89300ef602753cfe42a4)
Change-Id: I61477a7bc6e6bffe09dba79c37787b81bdc94a78