Fine tune the maganication area edit dialog

Root cause: The asset is not rectangle, it is high > width asset. Called the centerCrop cause the both dimensions (width and height) of the image will be equal to or larger than the corresponding dimension of the view (minus padding).
Solution: Change to fitCenter.

Bug: 146473544
Test: local test
Change-Id: I17de6a09f21e1454afcdd0297b81868c1b819de1