SF: fix a few bugs with FrameTargeter storing N fences

Bug: 267315508
Bug: 354007767
Bug: 308858993
Test: SF unit tests
Flag: com.android.graphics.surfaceflinger.flags.allow_n_vsyncs_in_targeter
Change-Id: Ib603c0fd29a3e4cb2fcd99dca59bbd5bfb55a787
5 files changed