Move config-at-end seamless-flip to activity-level

The current setup was made to sorta match pip1 in the
sense that the config-at-end task and activity surfaces
remain untouched and shell does a "forward" animation (ie.
it animates from identity to a transformed state) and
then WM flips the content and the surface transform
together at the *end* of the animation.

The issue, here, is that it means there is a period of
time where WM is manipulating surfaces (Task-level) that
Shell technically "owns" and without any synchronization
mechanism: this means shell can't synchronize updates
to it's overlay and also must somehow prevent user
interaction with the surface while WM is messing with
it; however, WM never tells Shell when it is done.

Instead of making the sync/communication more complicated
(and error-prone), we move the content/transform-flipping
to the Activity-level (which WM "owns"). This changes the
dynamics such that shell is now responsible for a
"catch-up" animation (ie. animating from a "reverse
transformed" state into the current state). The benefits
are:
* Works like other transitions now (which also do catch-up).
* WM only manipulates surfaces that it "owns"
* Synchronization is now only on start (like other transitions).
* No need to bubble-up CONFIG_AT_END flag.

We still keep the old behavior for activity-level because
there's really no other way to do it -- but activity-level
doesn't have the same issues as task because it is only
loaned to shell for the animation.

Bug: 202201326
Test: atest TransitionTests#testConfigAtEnd
Flag: com.android.wm.shell.enable_pip2
Change-Id: Ice26e2414772555fae577ce517a8892634e716da