Need to get a `GlyphSVG` instead of `GlyphColor`

[rcoreilly]

The addition of support for the COLR table in #196 breaks cogentcore's emoji font rendering, which is setup to process the GlyphSVG data. In Face.GlyphData, the COLR table has precedence, and there is no way to influence this behavior.

One strategy would be to add a field in GlyphColor that points to the SVG data if it is available? This is what GlyphBitmap does with the Outline field.

[benoitkugler]

Hum.. this is unfortunate. We (naively) did not think of consumers of Face.GlyphData with only partial support for glyph kinds.
I understand a fallback is necessary, but I'm a bit reluctant to add the SVG data because it only covers one fallback strategy : it won't help for say consumers who support only outlines.

Perhaps we could instead expose methods like
Face.GlyphSVG
Face.GlyphColor
Face.GlyphBitmap
Face.GlyphOutline
so that consumers may query the format they support.

[rcoreilly]

Yep that makes sense to me.