Flag: Trunk-stable flag for follower display backpressure handling for...

Flag: Trunk-stable flag for follower display backpressure handling for Pacesetter-driven arbitrary refresh rates

PDARR is comprised of three main changes:
1. "Greedy" follower display presentation via follower display backpressure
2. Migration of pacesetter display to the highest refresh rate display
3. Proper buffer release/transaction callback if a buffer is used across multiple displays

This CL introduces a flag for the "greedy" follower presentation/backpressure.

Refer to go/pdarr-1pager for details.

Flag: com.android.graphics.surfaceflinger.flags.follower_display_backpressure
Bug: 374072507
Test: N/A
Change-Id: I1d7cd167844d4b9411136610db95c2cf63323391