Noto Serif LGC support for Nuer language appears broken

@andjc wrote me

> Go to the Noto Serif specimen page, select Africa, then select under language dropdown Nuer to get the Nuer specimen.
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> (Screen Shots taken in Edge, but similar effect in Chrome and Firefox.)
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> Two different effects are seen.
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> In type specimen, you have font substitution for open-e and open-o .
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> In the waterfall you get the .notdef glyph instead
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> Nuer, like many African languages, needs one of the alternative glyphs for Eng, which unless the font is available is only accessible via aalt feature, a far from ideal solution for web fonts, a good solution for InDesign.
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> i assume that the type specimens are using GF version of the fonts, so are being subsetted, since the characters are in the font upstream

We can update the Extended Latin subset definition to add missing characters to the web font, if that's indeed the issue as I guess :)

> But I would suggest next time the Noto font pages are redesigned you explicitly detail for each language what opentype features they need to activate to get the glyphs needed for the language if not supported by default glyphs. Also worth noting that aalt works best with per character markup, if you are using a wide range of languages

Agreed, the way we handle and surface OpenType Features has lots of room for improvement :)