Emoji font support

[RoelN]

• Show emoji sequence as sample text
• Investigate why Noto Emoji's ligature combinations aren't shown in the OpenType features overview

[n8willis]

One possible idea for a default sample text would be to grab the Basic Emoji list, or part of it, and perhaps pull a few sequences from the different Recommended for General Interchange sets to test modifiers/ZWJ/regional-indicators.

Also might be useful to separate those sets, like you do with blocks, since there's a functional difference. A little less of a solid wall for casual readers, and it'd be slightly helpful for somebody debugging.

[n8willis]

the Basic Emoji list, or part of it, and perhaps pull a few sequences from the different Recommended for General Interchange sets to test modifiers/ZWJ/regional-indicators.

Should've put links in, for the benefit of future readers: https://unicode.org/reports/tr51/#Emoji_Sets

[n8willis]

It would also be useful to block fallback-font display for the Emoji codepoints that default to text-display mode.

In a plain-text, isolated-codepoint setting, the Emoji glyph doesn't get displayed but the user sees a text-mode glyph that comes from the fallback font instead, which gets confusing. (I observed this on Firefox with Noto Color Emoji in the non-beta site.)

Might be simplest to request emoji-presentation mode for those glyphs, but I don't know if there's a cross-browser way to prevent the fallback.