Complete COLRv1 and bitmap color rendering with tiny-skia

[xorgy]

Currently, we have an example of rendering with tiny-skia, but it does not support COLRv1 (because tiny-skia is missing certain gradient types) and it does not support bitmap color glyphs.

[nicoburns]

Some notes:

• The bitmap glyphs are (were?) a limitation of skrifa not having good support for extracting the bitmaps
• The COLRv1 was indeed because of tiny-skia missing gradient types. There was mention of these being implemented in some comments starting here, but if any work on that has been started then I don't think it is public

(@RazrFalcon is gradient types in tiny-skia still something you're planning to look into at some point?)

Previously written up here

[RazrFalcon]

Yes, I do plan adding Sweep gradients eventually. But no timeline in mind.

[yisibl]

Sweep gradients have already been implemented in linebender/tiny-skia#166