Don't allow PI-based starts and trampolines when sender

is SYSTEM_UID and it happens to pass foregroundness check
at the time of sending

It could lead to abuses like directing the user to Settings app
and then giving a PI through any API, so that app could open
activity/trampoline due to Settings app (SYSTEM_UID) being fg.

PI-based starts where sender is SYSTEM_UID will no longer be
supported based on foregroundness check. Any such starts need
to now be explicitly whitelisted (see b/124858756).

Also, ignore windows of type TYPE_APPLICATION_STARTING in
isAnyNonToastWindowVisibleForUid() check.

Bug: 129563343
Test: atest WmTests:ActivityStarterTests
Test: atest BackgroundActivityLaunchTest
Test: atest CtsActivityManagerDeviceTestCases:ActivityStarterTests
Test: atest WmTests:RootWindowContainerTests
Change-Id: I563f71f0b1c7922d8c675d2e4feed909f43446be