[svgcanvas] Add support for relative path encoding

 - expand SkParsePath to support relative path encoding
 - introduce a new SkSVGCanvas flag for clients to opt into relative
   encoding

Bug: skia:11981
Change-Id: I2d6c63254df23311f1a86dee9481bde9531c3b61
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/406876
Reviewed-by: Tyler Denniston <tdenniston@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
6 files changed