SF: Add TransactionHandler

- migrate transaction queueing and flushing into
  a new class and remove dependencies from
  other components.
- Add a filter interface for other components to
  participate in transactionready logic.

Test: presubmit
Bug: 238781169
Change-Id: Ia4da386cd72058126f6f765adafb9cb4d15b1d2b
13 files changed