Log Message:
libidn2: update to 2.3.2.

* Noteworthy changes in release 2.3.2 (2021-07-19) [stable]

** Upgrade TR46 tables from Unicode 11 to Unicode 13.
Now U+32FF works.  Fixes
<https://gitlab.com/libidn/libidn2/-/issues/77>.

** Fix build errors related to doc/idn2--help.texi.
With older makeinfo, this would manifest itself by looking for
idn2-help.texi instead.  Further, some BSD grep implementations did
not like the \+ regexp command, so we now rely on the (apparently)
more portable * regexp command.  Reported-By: David Gessel.  See
<https://gitlab.com/libidn/libidn2/-/issues/93>.

** doc: Improve GTK-DOC manual.

** doc: Don't ship HTML/PDF manual.  Drop custom CSS stylesheet.