Allow ActivityEmbedding to finish Activity through WCT

Before, we call Activity#finish() to finish activities when removing
TaskFragment. This may start a CLOSE transition before the organizer has
a chance to request the actual transition type.

Now, we allow the organizer to finish activities through WCT so that the
operation is atomic and the organizer can request the correct transition
type.

Bug: 240519866
Test: atest WmTests:TaskFragmentOrganizerControllerTest
Test: atest CtsWindowManagerDeviceTestCases:TaskFragmentOrganizerTest
Change-Id: I54671fb2dd34dca952468305429a90d89953de69