Refactor CoroutineScopeStore to PerDisplayRepository<CoroutineScope>

This will help in a follow up refactor of the keyguard

Bug: 362719719
Bug: 397680831
Bug: 403481022
Test: DisplayScopeRepositoryInstanceProviderTest
Flag: NONE - small refactor but no behaviour changes.
Change-Id: I2f29693def2219ca670cb5ca0691d49fb702c9fc