[3.9] bpo-46032: Check types in singledispatch's register() at declaration time ...

[3.9] bpo-46032: Check types in singledispatch's register() at declaration time (GH-30050) (GH-30254) (GH-30255)

The registry() method of functools.singledispatch() functions checks now
the first argument or the first parameter annotation and raises a TypeError if it is
not supported. Previously unsupported "types" were ignored (e.g. typing.List[int])
or caused an error at calling time (e.g. list[int]).

(cherry picked from commit 078abb676cf759b1e960f78390b6e80f256f0255)
(cherry picked from commit 03c7449fbc7c57f5e0365f234a0b65c1dde763f2)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>