Move underline thickness and position computation to Paint

Also, in TextLine, fix underline color and thickness to come from the
underline info rather than the TextPaint object.

Bug: 32907446
Bug: 62353930
Test: Manual
Test: cts-tradefed run cts-dev --module CtsTextTestCases
Test: cts-tradefed run cts-dev --module CtsWidgetTestCases
Change-Id: I259e9cf635a7056ccd367baa77c03100c69e3b98