Move rotation tracking to DisplayContent

This CL moves rotation tracking from WindowManagerService to
DisplayContent. This way displays can be rotated independently and
rotation of the main display won't affect rotation of secondary
ones.

Bug: 34242678
Test: android.server.cts.ActivityManagerDisplayTests
Test: testRotationNotAffectingSecondaryScreen
Change-Id: Ic46aaa523482b31ff5ec77f0c2908ceda1156fc0