RefreshRatePolicy: getPreferredRefreshRate should consider preferredRefreshRate

If an app set the WindowManager.LayoutParams#preferredRefreshRate, refresh
rate policy should return it the the preferred refresh rate of the window
if all the other signals (preferredDisplayModeId or deny list) doesn't
have a vote.

Test: atest RefreshRatePolicyTest FrameRateSelectionPriorityTests
Bug: 192413241
Change-Id: I55dc5c2acc8b66cfedbd0c0f0fb66c57eeaa36fe