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:1848b559059e021d1a923513ca2a936c6212a7ac)
Merged-In: Ibadc9c21f1d23f9904fc11009a9c2a40535db5e0
Change-Id: Ibadc9c21f1d23f9904fc11009a9c2a40535db5e0