end2end: Redo HWC observer presented/release events [16/N]

Instead of one event for both, where the bufferId's must be optional,
use two separate events, one for display, one for release.

Flag: TEST_ONLY
Bug: 372735083
Test: atest surfaceflinger_end2end_tests

Change-Id: Id3dc3362cae050466f4c746e1bd2662ee522893b