Fix various hw-accelerated line/point bugs

All accelerated lines are now rendered as quads. Hairlines used to
be rendered as GL_LINES, but these lines don't render the same as our
non-accelerated lines, so we're using quads for everything. Also, fixed
a bug in the way that we were offsetting quads (and not offseting points)
to ensure that our lines/points actuall start on the same pixels as
Skia's.

Change-Id: I51b923cc08a9858444c430ba07bc8aa0c83cbe6a