Fix bug 6892600 Font (character pairs) rendering issue

Alignment on paint for actual glyph drawing needs to always be left,
even when drawing centered or right aligned text. The x offset for
alignment is applied by OpenGLRenderer::drawText (and needs to be early
in the pipeline for quickReject to work). Similar change needed for
drawing drop shadow.

Also fixes bug with mispositioned underline (offset for alignment has
already been applied once, no need to do it again in
drawTextDecorations).

Change-Id: Id3dcd62de5536a26b158d768889273a1492b35d6