Reset display density ratio if forced density is called.

If setForcedDensityForUser is called after ratio has been set, ratio
must be reset as users are expected to either call
setForcedDensityForUser or setForcedDisplayDensityRatio.

Flag: com.android.window.flags.enable_persisting_display_size_for_connected_displays
Test: atest WindowManagerServiceTests
Bug: 407544305
Change-Id: I96e1878290b56d3ce7023e97daeae65f052ec848