Call minikin::getBounds instead of using Layout.

The bounding box is not necessary for drawing text, so it is
no longer stored in the Layout object. Instead, calculate by
minikin::getBounds function.

Bug: 169114687
Test: atest PaintTest
Test: atest Paint_TextBoundsTest

Change-Id: I3f77d2cc3843ac504c7475c7800f2526b403d933