Add initial implementation of GrShape and GrStyle classes and tests

The initial intent is to use GrShape to simplify the mask blur code paths. However, I also want to use this to explore a more unified drawing code flow for different geometry types. The goal is to have a single representation for geometries+styling that attempts to always keep the geometry in the simplest form (e.g. preferring rrects to paths). It also allows for converting styling information into modified geometry and for computing consistent keys.

BUG=skia:
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Review URL: https://codereview.chromium.org/1822723003
6 files changed