- Followup to #7694
- Disables the `traversal` feature of `skrifa` which is not needed
except internally by the fontations project
- Should save a little compile time, and possibly some binary size.

Signed-off-by: Nico Burns <[email protected]>

This adds support for rendering color emoji in egui via a new opt-in
`egui_noto_emoji` crate that bundles Noto Color Emoji sprites.

Key features:
- New `GlyphColoring` enum to distinguish color vs monochrome glyphs
- Color glyphs bypass text tinting and render with original colors
- Minimal API: `Context::register_color_glyph[_arc]` methods
- Atlas persistence: color glyphs survive font atlas rebuilds
- Deferred registration: glyphs registered before fonts init are queued

The implementation addresses feedback from PR emilk#7333 and emilk#7707:
- Fixes tinting problem (color glyphs not affected by text color)
- Handles atlas repopulation when fonts are recreated
- Aligns with skrifa+vello_cpu font backend (PR emilk#7694)
- Minimal API surface as suggested by @lucasmerlin

Co-Authored-By: Claude Opus 4.5 <[email protected]>

…7694)

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I'll probably come back to this and clean it up a bit. This PR
reimplements ab_glyph's functionality on top of Skrifa, a somewhat
lower-level font API that's being used in Chrome now.

Skrifa doesn't perform rasterization itself, so I'm using
[vello_cpu](https://github.com/linebender/vello) from the Linebender
project for rasterization. It's still in its early days, but I believe
it's already quite fast. It also supports color and gradient fills, so
color emoji support will be easier.

Skrifa also supports font hinting, which should make text look a bit
nicer / less blurry.

Here's the current ab_glyph rendering:

<img width="1592" height="1068" alt="image"
src="https://github.com/user-attachments/assets/2385b66e-23f8-4c6e-b8c2-ea90e0eea4e4"
/>

Here's Skrifa *without* hinting--it looks almost identical, but there
are some subpixel differences, probably due to rasterizer behavior:

<img width="1592" height="1068" alt="image"
src="https://github.com/user-attachments/assets/a815f3e9-65ac-4940-bc00-571177bef53d"
/>

Here's Skrifa  *with* hinting:

<img width="1592" height="1068" alt="image"
src="https://github.com/user-attachments/assets/d6cc0669-3537-4377-bba9-ed5ef09664db"
/>

Hinting does make the horizontal strokes look a bit bolder, which makes
me wonder once again about increasing the font weight from "light" to
"regular".

---------

Co-authored-by: Emil Ernerfeldt <[email protected]>

- Followup to emilk#7694
- Disables the `traversal` feature of `skrifa` which is not needed
except internally by the fontations project
- Should save a little compile time, and possibly some binary size.

Signed-off-by: Nico Burns <[email protected]>