Select fonts by requested emoji presentation

[kane50613]

LLM Contributions: Claude fact check + generates, Codex review.

Now font selection only checks for "who has the first char?". Variation selectors like U+FE0F are ignored, same for U+FE0E. It also happened in the downstream kane50613/takumi#1218.

Per candidate font, an exact cmap format 14 match for the whole sequence wins first. Otherwise U+FE0F prefers fonts with color tables and U+FE0E fonts without. When no font matches the requested presentation, the base character still renders from a mismatched font instead of tofu.

To check whether the font has color tables, I've mirrored ColorTableLookup from Blink.

#692 seems to be solving the same bug, but only by moving the emoji generic family to the front, which overrides user-selected fonts that have their own emoji glyphs. Checking each font's capability avoids that.

#620 is the segmentation layer above this and complementary.

Changelog

• Adds fontique::Charmap::map_variant, with MapVariant re-exported from read-fonts.
• Adds FontInfo::has_color_tables().
• Adds public QueryFont.has_color_tables.
• [Breaking change:] QueryFont struct literals must provide the new has_color_tables field.