Evas font-engine: Cache pen position instead of advance.

Evas font-engine: Cache pen position instead of advance.

We only really use adavnce for calculating the pen position, so it makes more
sense to just cache the pen_position instead and calculate advance from
that if ever needed.
This means size/advance calculations are now O(1) because we don't need to
walk the strings anymore.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/evas@58756 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33