fix(developer): Improve stability of named code constants

Fixes #4423.

Using a named character constant with a store name that included
characters outside ascii could cause kmcmpdll to crash with an assertion
failure.

This fix allows store names defined in the .kmn file to use characters
outside ascii.

Note that more work needs to be done on which characters are acceptable
to use, as this is somewhat implementation-specific according to the C++
specification for `iswalpha`.

Added a test case to verify various named code constant examples.

Also removes dead code for `IsCJKUnifiedIdeograph` as this was never
used and somewhat pointless in any case.

NamedCodeConstants.cpp could stand to be rewritten using `std::map` or
equivalent. Current implementation is pretty icky.