Send FrameTimeline packets as separate start and end messages

To avoid scoped slices, the FrameTimelineEvent proto was updated to
contain separate Start and End messages for SurfaceFrame and
DisplayFrame. This change updates the platform to send packets according
to the new proto.

Bug: 173426914
Test: libsurfaceflinger_unittest
Change-Id: I678f5b2b94109409b57d2ac61db704f77d149c76