[css-text][text-spacing] Extra spacing between Hangul and Hanja

[xfq]

https://drafts.csswg.org/css-text-4/#non-ideographic-letters

According to the current definition of non-ideographic letters, there seems to be extra spacing between Hangul and Hanja in Korean mixed script, but there shouldn't be.

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Example:

👆 text-autospace: no-autospace;

👆 text-autospace: normal;

[frivoal]

I think you're right: I thought that maybe Hangul would have the Han script property in Scripts.txt or ScriptExtensions.txt (but it doesn't), or be classified as F in EastAsianWidth.txt. (but it is W instead).

I wonder if we should fix this by including Hangul in the ideographs grouping, or by taking it out of non-ideographic letters. I guess that depends on whether we expect text-autospace: ideograph-numeric to inject spacing between Hangul letters and non-ideographic numerals. My guess would be that we do, and that even though they're not actually ideographs, typographically, Hangul syllables are largely similar to ideographs, and should be included in the ideographs grouping.

[frivoal]

Btw, I had forgotten about this, but see also #9503. We should make sure it does the right thing here.