Consolidate ActivityStack#finishCurrentActivityLocked checking

This CL is to fix a bug that found in
TransitionSelectionTests#testCloseTask_BothWallpaper_SlowStop may flaky
because when TopActivity launched & call finish(), the activity will destroy
too soon before BottomActivity resume & idle.

When TopActivity launched, suppose BottomActivity's nowVisible state should
be false because both activities are fullscreen activity & TopActivity should
cover BottomActivity.

After TopActivity called finish(), normally the activity should wait for
BottomActivity visible and then destroy, and this test is to verify if
TRANSIT_WALLPAPER_INTRA_CLOSE state will coming when opening & closing animation
target with wallpaper theme are animating case.

But the flakiness may happen if device is in low-performance stage, when
TopActivity launched, system calls setClientHidden for BottomActivity's all
windows to update its viewVisibility but can't update in time, and then
the next relayoutWindow comes, mis-detected BottomActivity's Floating child
window as drawn state, so that can't update BottomActivity's nowVisible
state as invisible with onWindowsGone().

So when TopActivity called finish(), TopActivity will soon going to destroy
state since BottomActivity is still in nowVisible state.

The fix is to add isNextNotYetVisible, if the next activity the nowVisible or visible
is not yet true, which means we need to add the current finishing
activity into stopping list and destory until the next activity idle.

Bug: 140088359
Test: atest TransitionSelectionTests
Change-Id: If1907d71135158bafea69881205f351ab666025e
Merged-In: If1907d71135158bafea69881205f351ab666025e