Flag: Trunk-stable flag for arbitrary refresh rate selection

The flag follower_arbitrary_refresh_rate_selection, when enabled, will
allow the follower display to be set to any of its refresh rate, rather
than one matching the pacesetter.

Refer to go/pdarr-1pager for details.

Flag: com.android.graphics.surfaceflinger.flags.follower_arbitrary_refresh_rate_selection
Bug: 371584290
Test: N/A
Change-Id: Ibae7bcf999412ef0623910515b88bd4f57312481