Dyno: Fix (callable variable, function) disambiguation

[DanilaFe]

This is a precursor to another PR, which enables resolution of more of the domain module code, and finds this curious case that doesn't work in Dyno:

proc foo(x: int) {}
proc bar(foo: (int, int)) {
  var res = foo(0);
}

In production, we expect the call to foo in the body of bar to be a tuple element access, but dyno incorrectly attempts to perform full function resolution. This is difficult since the inner foo is not a function.

In production, we resolve this problem by stopping the search for functions when we encounter a variable. In the case of an innermost variable, this is sound since variables are not overloaded or disambiguated (innermost is preferred). In the case of functions, this is sound because any functions defined after the variable during the search must be more distant in terms of scopes, and thus would be rejected in favor of "nearer" functions.

I chose to implement this behavior in Dyno, particularly because of a TODO by @riftEmber that seemed to be adjusting for this kind of behavior. To do so in the most performant way (i.e., without iterating over the list of found IDs to see if any were variables), I adjusted all the lookup procedures to return a LookupResult instead of a boolean. This type is boolean-like (it supports operator bool and |=), but it contains two booleans, one of which is whether a variable was found. From there, I adjust the early-return logic (previously: innermostOnly && got) to also handle the case of "I found a variable so I should stop looking".

The only tricky aspect is detecting ambiguity, in which we found a function and non-function at the exact same place. We need to report an error when a variable and a non-variable were found since the last "return point" (last check for innermostOnly && got etc.). For this, I did fall back to an iteration: if a variable is detected in a scope, and there are several copies of that variable, it's almost certainly an error.

Reviewed by @riftEmber -- thanks!

Testing

• dyno tests
• paratest