Removing references to hidden classes in shared lib.

- Restructure assist data receiver to not extend hidden interface
- Restructure animation spec to not use hidden spec class
- Restructure transitions apis to not use graphic buffers
- Remove direct arguments which use hidden animation start listener
- Renaming some methods to be a bit more clear
- Expose AnimateableViewBounds and task stack listener

Bug: 67510855
Test: Sysui and quickstep still build and work
Change-Id: Ibc471c34a725daa3149765960ae0731996ceb854