Signature for built in calls

[fbs]

I wonder if its doable to write a simple spec for each call that handles this and all the other standard check things for calls (and builtins). E.g.

CallSpec {
 .name = "str",
 .probe_types = any,
 .required_features = {somefeature},
 .min_args = 1,
 .max_args = 2,
 .arg_types = [
  [{ type = integer, literal = true}, { type = pointer } ], // arg0
  [{ type = integer }], // arg1
  .func = &semantic_analyser::call_str
]}

It would remove quite a bit of basically duplicate code everywhere, the deep nested long functions and would help standardize error messages. It should also make it easier to get a quick overview of the calls we have an what kind of arguments they take, might even be possible to generate nice help format output from it.

But there probably are some cases that make it hard to do

Originally posted by @fbs in #1646 (comment)

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This should of course integrate with the existing type system, maybe in the form of a new Function type.