Add COLRv1 palette querying, switching, and custom setting hooks

[HinTak]

See https://typedrawers.com/discussion/5105/is-anyone-actually-using-color-fonts and
https://github.com/kyamagu/skia-python/blob/main/patch/skia-m123-colrv1-freetype.diff , especially the "palette" argument/area.

[HinTak]

This is mostly a reminder for myself and/or good first issue for new external contribution.

[HinTak]

Just to be explicit - it is still my suggestion to remove the COLRv1 patch (and the other stub in font.cpp) if I disappear/unresponsive for any lengthy period.

[HinTak]

I had a small update to the colrv1 patch to expose the font descriptor in m129 which was only posted in my skia-building-fun repo (now included here in the m132 update), but it looks like upstream in m132 provides a different way of accessing the palettes via #282 .