[canvaskit] Add Path2D to Canvas API

This moves the shared logic into path2d.js from
canvas2dcontext.js.

Bug: skia:
Change-Id: Id63bc52a190109f7cbc4e17ddb5603e6e87d5dc0
Reviewed-on: https://skia-review.googlesource.com/c/178268
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
8 files changed