Add preferredMaxDisplayRefreshRate

Add a new private window attribute for allowing apps to specify the max
display refresh rate. This is useful for use cases such as keyguard
where the refresh rate should be limited to preserve power.

In the next CLs the preferredDiplayModeId would be enabled for
frame rate override (60-on-120) and the preferredMaxDisplayRefreshRate
would be the alternative to control the display refresh rate (as opposed
to the frame rate experienced by the app).

Test: atest RefreshRatePolicyTest
Test: atest DisplayModeDirectorTest
Test: Launch camera app and observe refresh rate
Bug: 183226498
Change-Id: I1c5e9f6047cbea4bfb581251b8dd2b9058b3e378