Update Pip launches to not enter pinned task if in background.

Addresses a BAL bypass where Pip could be started without the launcher
being visible.

Bug: 271576718
Test: atest CtsWindowManagerDeviceTestCases:PinnedStackTests
Test: atest android.server.wm.BackgroundActivityLaunchTest#testPipCannotStartFromBackground
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b263d3beed7a412ac342c63956f213b70d6e2679)
Merged-In: Icfe0a17d7f6f127acaae8400a97e8bdc53fcc9ad
Change-Id: Icfe0a17d7f6f127acaae8400a97e8bdc53fcc9ad