Update Unicode mapping tables to current versions

The primary motivation for this is to resolve a licensing issue with
these files (the files have been relicensed with a Debian-approved
license), but there were a few minor fixes/additions since the previous
update.  The generation code/scripts required some modernization to get
it working on a current system, as well as needing to handle the format
of CP866.TXT, which is a bit different than the other files.

Update the whitespace check to exclude these files from it as we prefer
not to modify them to avoid any divergences with the upstream copies
(even trivial ones).

Closes #26700.

.github/workflows/code_checks.yml

@@ -59,6 +59,7 @@ jobs:
                 ':!build/vcxproj-clone' \
                 ':!docs/doxygen/doxygen-awesome-css/*' \
                 ':!misc/languages/data/unicode/*.xml' \
+                ':!misc/unictabl/mappings/*.TXT' \
                 ':!samples/widgets/widgets.bkl' \
                 ':!tests/test.bkl' \
                 ':!**/*akefile*' \