SF: Allow mode change request in scheduler without pacesetter mode change

Currently, Scheduler::applyPolicy() ignores results from the
RefreshRateSelector if the desired pacesetter mode has not changed,
even when other displays' desired modes have changed.

This means that things like touch boost and idle based refresh rate
adjustment would get ignored if the display is not the pacesetter.
This does not make sense in a world where SF can drive multiple
displays at different refresh rates (so long as the pacesetter remains
the fastest display)

This CL changes the behavior so that any changes between the desired
display mode and the current active display mode on any display will
trigger a mode change request.

Flag: com.android.graphics.surfaceflinger.flags.follower_arbitrary_refresh_rate_selection
Bug: 371584290
Test: 75Hz external, 120/60Hz internal; play video on internal and leave idle for 60hz,touch boost to 120
Test: new SchedulerTest unit test cases
Change-Id: I54adbb01a5f653fd73ef141cd9101f625129595b