fastuidraw/painter/stroked_path: add inner bevels
fastuidraw/painter/stroked_path: add inner bevels

Add inner-bevels that are needed when stroking with a stroking
radius that is greater than the "radius of a curve", i.e. when
stroking so widely, that the rectangles on the inside of curves
invert.

Change-Id: I206e27f6deaf4fe63f4f6d900afb064dbba1b15f

01org/fastuidraw,01org/fastuidraw