SF: Track and consider all displays for mode change pending state

Currently, only the front internal display's mode change status is
considered when Scheduler::setModeChangePending() invokes
LayerHistory::setModeChangePending().

This CL introduces per-display mode change pending tracking in the
Scheduler, and changes the LayerHistory's mode change pending state to
be true if any of the display in the system has a mode change pending.

Flag: com.android.graphics.surfaceflinger.flags.pacesetter_selection
Bug: 255635821
Test: manual w/ dumpsys && SchedulerTest && RefreshRateSelectorTest
Change-Id: Id50791c64c6fd354d983b2e455760f55b89d286c