Merge "Revert^2 "libui: rewrite Region with FatVector"" into rvc-dev am: 5b7d7e2150 am: 7b1930a89c am: 9a3ed149e7 am: 6bfa610134

Change-Id: I155271501bb53f3f38d6aafba4b28f94d73d1ec1