Deprecate variadic arguments to macro #raise

[Blacksmoke16]

Wanted to create this issue before opening a PR.

Currently you can call macro raise with 0 or more arguments:

{%
  # No arguments
  raise

  # Multiple arguments
  raise 10, "foo", false
%}

Additionally you can pass whatever kind of argument as well. I think it would make sense to deprecate the ability to call it with 0, or more than 1 argument. We can raise a warning in the meantime.

We could also go a step further and require the argument to be a StringLitereal, raising a separate warning for that if we so desire.

Originally posted by @Blacksmoke16 in #13262 (comment)

[straight-shoota]

Sounds good. I don't see a relevant use case for multiple arguments. Runtime raise doesn't have that either.
Although this behaviour was implemented from the beginning: 9e26cf9
@asterite Do you have any recollection why multiple arguments are allowed and joined?

Not sure if a deprecation warning gets much attention in the case of a macro raise, but we can try it =)

[Blacksmoke16]

And what about the implicit string casting? I.e. should we also enforce you pass only strings to it or is to_s whatever you pass it expected?

[straight-shoota]

I guess implicit casting shouldn't really be necessary. We can probably drop it. Not sure if it matters much, though.
Same goes for the variadic arguments: There's no problem with having this feature. Removing it is just for cleaning up a bit.