Unbreak hyphenated prefixed names

[mmarx]

Consider foo.ttl with

@prefix eg: <https://example.org/> .

eg:foo eg:a-property 42 .

and a program

@prefix eg: <https://example.org/> .
@import triple :- turtle{resource="foo.ttl"} .

foo(?x, ?y) :- triple(?x, eg:a-property, ?y) .
@export foo :- csv{resource=""} .

This will not output anything, since - is no longer allowed as part of names (cf. #545). It will also not output any diagnostics. We have thus traded an unwarranted (yet, arguably, helpful) diagnostic

result(?arithmetic-1) :- fact(?arithmetic) .
       ──────┬──────
             ╰──────── unsafe variable used in rule head: `?arithmetic-1`

Help: a variable with a similar name exists: `arithmetic`

Note: every universal variable in the head must occur at a safe position in the body

that makes it quite obvious what the issue is (and how to fix it) for silently ignoring parts of the program. From a user experience standpoint, this is much worse. Also note that the same issue as #543 still persists with %, which we still allow in names (it's used for escape sequences in prefixed names). This is also even worse than the potential problem outlined in #545 and #546, in that I can easily change the prefix names I define in the program, but I have to work with the local names I get from upstream RDF graphs, and always using fully expanded IRIs is a terrible experience.

First of all, we should probably not treat variable names, plain constants, and prefixed names the same – there's no good reason a variable name should be able to contain a - or an % (there might be other characters that cause confusion with builtin operators as well). Second, we should have diagnostics for clearly ill-formed rules: subtracting a constant from a constant should be a syntax error (or, at the very least, a warning) – how could this ever be interpreted as a valid rule (note that, e.g., this problem doesn't arise in SPARQL, as constant names are not allowed in arithmetic expressions there)? This would then allow us to accept - and % in both the prefix name and the local name of a prefixed name.