Detect Remove-pip transaction to properly close multi-activity pips

Multi-activity pip converts setWindowingMode(UNDEFINED) into a
"reparent pip activity + move-to-front" when expanding pip. Shell
doesn't know whether a pip is multi-activity or not, so it just
makes a WCT with setWindowingMode(UNDEFINED) AND reorder-to-back.
The problem is that setWindowingMode happens first which triggers
the "merge + move-to-front" logic -- the reorder command was
for the unmerged task so it just gets ignored.

This CL basically checks if the WCT also has a move-to-back in
addition to setMode(UNDEFINED) and, if so, uses the "workaround"
found in removePinnedRootTaskInSurfaceTransaction to prevent
setWindowingMode(UNDEFINED) from doing the wrong thing: it sets
FORCE_HIDDEN_FOR_PINNED_TASK.

Bug: 232954259
Test: open multi-activity pip (eg. ApiDemos). Go to pip. close it
      via the X button.
Change-Id: Iaafbc1c930eb1bcfb427533ae28ef9a823d6b9c6