Add preferredMinDisplayRefreshRate

Add a new private window attribute for allowing apps to specify the min
display refresh rate in addition to the existing
preferredMaxDisplayRefreshRate. This is useful for use cases such as
keyguard where the refresh rate should be limited to a single value,
and using preferredDisplayModeId would not lock the display
refresh rate, as frame rate override might be enabled.

Test: atest RefreshRatePolicyTest FrameRateSelectionPriorityTests DisplayModeDirectorTest
Bug: 183226498
Bug: 184176119
Change-Id: I343569b3cbccd73001703dca78f0f99e196a4d52