Implement equals and hashcode for MediaSessionRecord(s)

- This involves changing MediaSessionRecordImpl into an abstract class.

Bug: 295518668
Bug: 297052684
Test: atest CtsMediaBetterTogetherTestCases MediaRouter2HostSideTest
Change-Id: I1f7f9da7c689093ab5df6ef26d255e56c36486f7
4 files changed