Updated ColorDrawable to implement getColorFilter

ColorDrawable previously did not implement getColorFilter despite having
a proper setColorFilter implementation. Updated ColorDrawable to support
getColorFilter returning the corresponding ColorFilter configured on
it's paint.

Change-Id: Iabc3cd1b9110f5c3ec25e26a31966e2a43f8fb16
Fixes:78476471
Test: Re-ran CtsGraphicsTest