MotionTestRule: Adding TimeSeriesSubject for diffing TimeSeries and producing a readable diff.

Updated the [TimeSeries] to expose the features via map instead, and
adding toString implementations for better readability of diff outputs

go/android-animation-tests-design

Test: Unit tests
Bug: 322324387
Change-Id: Ie22773d77d1d34917cc355380836f12c76897b6c
7 files changed