Move default pip position to right above the shelf.

This change takes care of the flow from WindowManagerService to
PinnedStackController, all the way to PipTouchHandler. It also
introduces a WindowManager hook that allows Launcher to pass in
shelf visibility and height. A separate change is made to send
signals from Launcher to SysUI. (ag/3724896)

Bug: 73961893
Change-Id: I2ff54e78bc2dc35c806b902464048b051a4d6394
Test: atest CtsActivityManagerDeviceTestCases:ActivityManagerPinnedStackTests