[WIP] Piet skia

[pum-purum-pum-pum]

Adds skia backend to piet

Current TODO list

• fix paragraph/simple text font inconsistency (for some reason in skia Paragraph and draw_string uses different defaults for fonts) ~* "XI" image logo example not working (I found it in my druid fork which works with skia)~
• add snapshots
• clean up code and commits history
• use skia crate (currently it's also fork that is not fully upstream yet)

Also useful links: druid fork with winit for testing this backend https://github.com/pum-purum-pum-pum/druid

[cmyr]

@pum-purum-pum-pum I'm happy to treat this as a "second tier" backend, and not include snapshots? This is how (for instance) the svg backend works. You should still have an example program that can run the sample images, though; you can probably just adapt one from another backend.

I think we'll also want to add this to piet-common, although we'll need to figure out how to make it selectable; a feature flag would work but we tend to have a bad time when we try to use a feature to toggle between two implementations...

In any case, looks like you've made some good progress, will be happy to give this a more careful read when you've got the sample images working. :)

[pum-purum-pum-pum]

This is most likely postponed until Skia will have a new release. Because skia-safe fork that I'm using currently relies on the master branch Skia.

[cmyr]

@pum-purum-pum-pum sounds good, please ping me in a comment when this is ready for a look!