[css-text-4] text-spacing-trim and classes of closing punctuation

In css-text-4 8.5.1. Fullwidth Punctuation Collapsing, we have:

Set fullwidth closing punctuation half-width if the next character is any of:

• a fullwidth closing punctuation
• a fullwidth middle dot punctuation
• an ideographic space (U+3000)
• a fullwidth opening punctuation of a larger font-size
• a character belonging to Unicode general category Pe

I think we should we add Pf alongside with Pe.

These WPT tests assume it, and that seems very reasonable to me:
https://wpt.fyi/results/css/css-text/text-spacing-trim?label=master&label=experimental&aligned&q=text-spacing-trim-quote-001.html

Further, thoes tests makes it conditional on the language, collapsing when it's Japanese, but not when it's Chinese. If we were to do spec that language dependency, it should be for more than just Pf, but also Pe and Ps (in the previous rule). Or maybe we don't need the language dependency, and the variants of those glyphs that can or cannot be trimmed can be detected from the font?

cc: @fantasai @kojiishi

Read css-text-4 §8.5.1, “Fullwidth Punctuation Collapsing,” and inspect the linked WPT text-spacing-trim tests, especially text-spacing-trim-quote-001.html. Resolve whether Pf should be added, how Pe/Ps/Pf behavior depends on language, and whether font-specific variants affect the rule; done means the specification and corresponding tests agree.