SF: Simplify Scheduler's hardware VSYNC delegate

As a step toward hiding implementation details of how Scheduler handles
changes in a display's power mode (e.g. toggling of hardware/synthetic
VSYNC), move and rename SurfaceFlinger::setVsyncEnabled to Scheduler::
onHardwareVsyncRequest. This hides setPendingHardwareVsyncState.

(getPendingHardwareVsyncState will be moved to Scheduler later.)

Store the per-display hal::PowerMode in Scheduler. On power mode change
in SurfaceFlinger::setPowerModeInternal, update the Scheduler for every
display, not just the active display.

Inject the delegate into VsyncSchedule's constructor, instead of passing
the (partly unrelated) ISchedulerCallback to several member functions.

Bug: 271431077
Bug: 241286146
Bug: 255635821
Bug: 241285191
Test: FoldableTest
Change-Id: I157b0895a77f055763f86dd21602d0dac13622da