Without explicit annotation, some type checkers infer that the type of
the 'default' argument can only be type[KeyError]. This was the case
in unicodedata_test.py, where pyright disallowed "LTR". This commit adds
annotations to avoid this, fixing the issue in the test (and external
code dependent on the API).
Some of the other functions in this file have the same semantics and
suffer from the same type error, and so this fix could also be extended
to them as usage requires.
9bfb72b055