Dedup predicates to check if remote animation target can be created.

The predicates below were used to check if remote animation target could
be created from a WindowContainer.

- WindowContainer#canCreateRemoteAnimationTarget
- WindowContainer#canBeAnimationTarget

The former was used by WM shell transition and the later was used by the
legacy transition. Merged the predicates.

Test: no-op refactoring. Existing tests pass.
Bug: 235601859
Change-Id: I985605b0c1eba22be16a32db6294e9623ea84705