Synthetic modes are respected when returning default refresh rates

For VRR panels defaultRefreshRates will include refresh rates from synthetic modes
This will allow RefreshRatePolicy properly set minSupportedRefreshRate for VRR displays

Flag: EXEMPT bugfix
Bug: b/340999835
Test: atest RefreshRatePolicyTest, manual testing
Change-Id: I64e40a7a7e1cbb441c7041fbcb07ea7d5350694b