SF: Match followers' refresh rate to pacesetter's

Multi-display refresh rate selection was flawed: The scheduler runs the
refresh rate selection algorithm for each display, and then filters the
candidate modes of each follower to match the pacesetter's refresh rate.

This means that:

1. The followers incorrectly consider refresh rates that don't match the
   pacesetter. Because the DM-specified constraint is [59, 61] Hz, some
   situations caused selection of a fractional rate (e.g. 59.94) instead
   of 60 on certain external displays. The result would be black screens
   for several seconds due to mode sets if the selection was not stable.

2. The followers incorrectly evaluate heuristics that should only affect
   the pacesetter, e.g. per-surface votes, global signals.

Fix this by teaching RefreshRateSelector about follower displays.

Foldables also benefit from no longer running the algorithm twice.

Fixes: 324188430
Bug: 329111930
Test: No black screen for 4 seconds upon rotating mirrored YouTube.
Test: 60+60 still works on foldables.
Test: RefreshRateSelectorTest.pacesetterConsidered
Change-Id: Ie1b27e81d860a709c85651f068fedb2b496861de