SF: Reset VsyncModulator on active display change

Between VsyncModulator::onRefreshRateChange{Initiated,Completed}, if the
active display changes, the newly active display's VsyncConfiguration is
propagated to VsyncModulator via updatePhaseConfiguration, which selects
VsyncConfigType::Early due to the `mRefreshRateChangePending` of the now
inactive display.

Clear `mRefreshRateChangePending` and let `onRefreshRateChangeInitiated`
set it for the newly active display if needed.

In practice, the end result is the same due to the forced modeset for an
active display that was just powered on. However, this will no longer be
true with concurrent displays when the new pacesetter is already powered
on.

Bug: 255635821
Test: DisplayModeSwitchingTest.multiDisplay
Change-Id: If264742a107cf5839d2c820eab23712778c1ae2e