Revert "libui: rewrite Region with FatVector"

Revert submission 10248126-fatvector-region

Reason for revert: b/149254345
Reverted Changes:
I09dc2fddd:hwui: remove FatVector
I265c6c831:libui: rewrite Region with FatVector

Change-Id: I2697cea4d4714592fa6a1f170b53ff51d2d62714

Test: boots
Bug: 149254345
Change-Id: Ib60dbf3ef41d6439fba095e3e905580bb59d3739
5 files changed