vt: introduce gen_ucs_fallback_table.py to create ucs_fallback_table.h

vt: introduce gen_ucs_fallback_table.py to create ucs_fallback_table.h

The generated table maps complex characters to their simpler fallback
forms for a terminal display when corresponding glyphs are unavailable.
This includes diacritics, symbols as well as many drawing characters.
Fallback characters aren't perfect replacements, obviously. But they are
still far more useful than a bunch of squared question marks.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20250507141535.40655-5-nico@fluxnic.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>