Optimize text and support group rect

[jonmmease]

This PR does a few things:

1. It improves the performance of the text mark by sharing the FontSystem and SwashCache across marks.
2. Fixes the coloring of emoji
3. Sets default font families to better match vega/vl-convert
4. Adds support for stroke/fill for group marks.
5. Adds pixi config in preparation for Python support

Here's an example rendered by this PR:

[jonmmease]

vl-convert doesn't handle emoji, so we're not actually trying to match this baseline