Modernise charnames (and _charnames)

[JRaspass]

charnames is the public pragma and gets the following changes:

• Move the version declaration into the package line.
• Use v5.40 to get strict, warnings, sub sigs, and module_true.
• Use unicore::Name isn't needed, and is removed. It predates the charnames/_charnames split and _charnames loads it itself.
• sub sigs replace manual arg validation in a couple of places.
• import() and viacode() are created without needless wrappers.

_charnames is the internal module which shouldn't have outside callers so we're free to make more backwards-incompatible changes:

• Move the version declaration into the package line.
• Use v5.40 to get strict, warnings, sub sigs, and module_true.
• sub sigs replace manual arg validation in a couple of places.
• Various subs have been made lexical if they have no outside callers.
• alias() is now consistently called with a hash.
• Prototypes were replaced with sub sigs in a couple of subs. No caller calls without parens which might benefit from a prototype.
• alias_file() had an unused arg which was removed.
• A c-style for loop became simpler by switching to a foreach.
• viacode()'s use of caller was adjusted by one stack frame as it's only ever called as charnames::viacode() which no longer wraps.

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• This set of changes does not require a perldelta entry.