Always SeqId client draws prefactors [1/n]

Some (p)refactors that just add/rename/rearrange some
things. No functionality is added/changed here. This
CL is mostly to separate out non-functional changes
so that review is easier.

Some of the changes:

- add seqId parameters to the Core<->Client interface
- remove forceReport from WallpaperService which was
  always false.
- separate out some declarations from assignments in
  preparation for flagged branching.
- remove syncNextBuffer from WC since only used in
  WindowState
- adjust some tests to look for effects vs methodcalls

Bug: 385976595
Test: existing tests updated
Flag: EXEMPT mechanical refactors
Change-Id: Ie55f4f1afb3a54ced8088915095bc251665aa0fd