offset angle check edge in common

offset angle check edge in common

When curves cross, their intersection points may be nearby, but not exactly the same.
Sort the angles formed by the crossing curves when all angles don't have the same
origin.

This sets up the framework to solve test case that currently fail (e.g., joel6) but
does not fix all related test cases (e.g., joel9).

All older existing test cases, including extended tests, pass.

Rework the test framework to better report when tests expected to produce failing
results now pass.

Add new point and vector operations to support offset angles.

TBR=reed@google.com
BUG=skia:6041

Change-Id: I67c651ded0a25e99ad93d55d6a35109b3ee3698e
Reviewed-on: https://skia-review.googlesource.com/6624
Commit-Queue: Cary Clark <caryclark@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>