Some code cleanup of InteractionJankMonitor.

- Move the CUJ constant related stuff to its own class
- Remove the Session class
- Separation of IJM and FT via event listener, breaking the dep loop
- Fix (unlikely) race problems in begin/cancel/end
- Trim out some unused stuff
- Remove some duplicated stuff (like config validation)
- Remove checks ensured by tests
- Fix a bunch of warnings
- Fix missing locks in debug overlay
- Remove the outdated DEBUG mechanism

Test: atest com.android.internal.jank
Flag: NA
Change-Id: I29b9da107313d4c07777ce50ce907c7516258807