[canvaskit] Add createPattern support to canvasAPI

Add Changelog to start tracking API changes (in preparation
for NPM)

Simplify globalAlpha passing.

API change:
 - Make ImageShader take an SkImage instead of encoded bytes.

Bug: skia:
Change-Id: I716f001b54ed58da3f40ae4e060b7098b550af9f
Reviewed-on: https://skia-review.googlesource.com/c/175260
Reviewed-by: Florin Malita <fmalita@chromium.org>
7 files changed