Dyno: implement removed cast copy behavior

[DanilaFe]

Closes https://github.com/Cray/chapel-private/issues/7329.

This causes the following program to cause a copy initialization of a:

record R {
}
proc consume(ref x) {}

proc test() {
  var a : R;
  var ret = a:R;
  consume(a);
  return ret;
}
var x = test();

The error in the original issue was resolved by @benharsh as of #27486; the program in the example works under --dyno-resolve-only. The key contribution of this PR is the invocation of the copy initializer, which production introduces via a call to _removed_cast, which has an in intent.

In the spirit of dyno -- where we try to avoid odd calls to unexpected internal functions -- this PR does not replicate the call to _removed_cast. Instead, it simply detects the auto-implemented redundant cast (added in #27486) and invokes the in-intent handling logic.

Generally speaking, once call resolution is completed, there's no way for the Resolver, or any other code, to detect how the resolution was performed. I was faced with a choice between implementing a general signaling mechanism (e.g., storing an enumeration for "how was this resolved" in CallResolutionResult or detecting the auto-cast as a special case. For now, lacking enough examples of how a general mechanism would be useful, and given how easy special-case detection is, I went with the special-casing. As a result, the VarScopeVisitor -- which performs the call to the in-intent handler -- has to do some sleuthing, detecting calls to : where no function candidate was detected.

Testing

• dyno tests
• motivator now produces a copy
• paratest
• paratest --dyno-resolve-only

Reviewed by @benharsh -- thanks!

[benharsh]

Nice! This should also help quiet down some of the noise in the typed converter.