Display-level relative display rotation should be 0

Because duh. DisplayContent is root, so it can't have a
relative rotation.

The problem is that RootWindowContainer ends up with the
default display's rotation because we store the "global"
configuration at that level. This is a legacy thing, so
until we clean that up, we have to just fix things at the
display level.

Bug: 249250882
Test: atest ChangeAppRotationTest, look at the trace and see that
      the recording display doesn't get rotated.
Change-Id: I76dc12be8ba934799dbc2ade3e00476f73bf3c71