Track pendingBuffer count in RequestedLayerState

Allows for easier retrieval without added lock contention.
RequestedLayerState stores a pointer to the original
buffer count from legacy layer.

Bug: b/294922229
Test: presubmit
Flag: EXEMPT, mechanical refactor
Change-Id: Iaab1b2214cc670f6e2d385ba4aba31e635a34030
6 files changed