bug#47857: fill-paragraph vs. FULLWIDTH DIGITs: bug exposed

[積丹尼 Dan Jacobson]

Disaster! M-q runs the command fill-paragraph

And turns:

Today's lucky number(s)!:
９
１０
１１

Into:

Today's lucky number(s)!:９１０１１

OK, if it is so smart, then why doesn't it also turn:

Today's lucky number(s)!: ９ １０ １１

into:

Today's lucky number(s)!:９１０１１

Well, surprise, it was actually very happy with ９ １０ １１ all along.

OK, let's add some space:
Today's lucky number(s)!: ９         １０ １１
becomes:
Today's lucky number(s)!: ９ １０ １１
perfect.

Anyway if it were stable in its output, then one would always get the same
results. Bug exposed!

(Yes, even LC_ALL isn't going to help. And yes, all this works fine if
all this was good old ASCII. emacs-version "27.1".)