Feature Request: Support tone marks (diacritics) used in Pe̍h-ōe-jī and Tâi-lô #776
Description
Description of the new feature/enhancement (with images if possible)
Pe̍h-ōe-jī and Tâi-lô are systems used to write Hokkien in romanized forms. Both systems use diacritics to mark tones, so any vowel or syllabic consonant can have diacritics. It seems that most fonts don't fully support them because of combinations of base characters and diacritics not found in western languages.
Tauhu Oo has a list of characters which have to be supported:
https://tauhu.tw/gua-ji-pio/#%E5%8F%B0%E8%AA%9E%E7%BE%85%E9%A6%AC%E5%AD%97
Tauhu Oo 20.05, a non-monospace font made to support all languages in Taiwan. It is based on Source Han Sans.
Iân-sui 1.002, another non-monospace font made to support all languages in Taiwan.
Cascadia Code 2404.23: Various tone marks on I, U, O, M, N are not supported. The vertical line (U+030D COMBINING VERTICAL LINE ABOVE) is not supported.
Cascadia Next TC: It looks worse than Cascadia Code.
Proposed technical implementation details (optional)
Sorry, I don't have font development skill.