Call minikin::getBounds instead of using Layout.

This is a 2nd attempt of I3f77d2cc3843ac504c7475c7800f2526b403d933

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: Ib7c132b1d65369af54b636155c3bdb675415ea55