bug#69968: Case-folding of Mathematical Alphanumeric Symbols

[Juri Linkov]

I wonder why case-folding is not supported for letters from
the Unicode block "Mathematical Alphanumeric Symbols":
https://en.wikipedia.org/wiki/Mathematical_Alphanumeric_Symbols

Is it because the Unicode standard doesn't provide information
about their case-folding?  And indeed they are missing from
https://unicode.org/Public/UNIDATA/CaseFolding.txt

But OTOH, I can't find the file CaseFolding.txt in admin/unidata.
This means Emacs doesn't use this file?

Then should we add more case-folding information explicitly
for this Unicode block?

Case-folding is already supported for some characters from other
Unicode blocks such e.g. FULLWIDTH LATIN CAPITAL LETTERs,
CIRCLED LATIN CAPITAL LETTERs, etc.
But e.g. PARENTHESIZED LATIN CAPITAL LETTERs are missing too.
What is worse is that in Emacs ⒜ doesn't have even a word syntax
like its counterpart 🄐.