Start moving text measurement into native code

We want to move text measurement into native code, mostly so that
alternate measurement for hyphens can be performant. This patch begins
that migration, in the main StaticLayout case, but still surfaces the
widths array to Java (for ellipsis calculation), and also includes a
hack (used mostly for testing) for computing widths in Java and sending
them down to native code when TextPaint is subclassed.

Change-Id: I476c9e8b3aa8e4e3552eb18f66c4bcd5683f3a72