[3.13] gh-80667: Fix case-sensitivity of some Unicode literal escapes (GH-107281) (GH-144754)

Lookup for CJK ideograms and Hangul syllables is now case-insensitive,
as is the case for other character names.
(cherry picked from commit e66f4a5a9c7ce744030d6352bf5575639b1096cc)

Co-authored-by: James <snoopjedi@gmail.com>