Simplify ScreenshotController/ViewProxy interface

Moves the internal insets and onAttachStateChange listeners into the
view proxy, since these don't depend on the ScreenshotController
directly and can be handled internally.

Bug: 329659738
Test: manual, atest
Flag: NONE
Change-Id: Ic87f36708b7a01e693bc134c0dc4043a5bfb4251
Merged-In: Ic87f36708b7a01e693bc134c0dc4043a5bfb4251