Fix transparency seekbar in accessibility button page is backwards

Root Cause: Store value in opacity value, need to be inverted to
transparency value.

Solution: transfer to transparency value and rename related field.

Bug: 183980065
Test: atest FloatingMenuTransparencyPreferenceControllerTest
Change-Id: I763dda47854e7cf945a95f4a7d4965725cd73824
3 files changed