Better Minikin integration

This patch improves the Minikin integration in a number of ways,
including:

Software rendering does text decorations and handles alignment
correctly. This fixes bug 15139067 "Centered text isn't working".

Paint implements getTextPath. This fixes bug 15143354 "Text rendering in
Maps Navigation wrong typeface?"

Also a bit of refactoring, since there was duplicated code for iterating
font runs that's now a static method in MinikinUtils.

Change-Id: I4cfdb2c0559982376348325a757d95235fab1768