Analyzer doesn't forward const constructors

[fishythefish]

See #32223.

class Mixin {}

class Base {
  const Base();
}

class Sub = Base with Mixin;

void main() {
  const Sub();
}

Analyzer incorrectly produces an error: The constructor being called isn't a const constructor.

[scheglov]

I have issues with understanding the spec wording, asked for clarification.

[srawlins]

Erik responded in that issue.

[eernstg]

I think we can close this issue, based on the title. In particular, the analyzer (and the CFE) do create/assume the required forwarding constant constructors, such that the following updated example has no errors:

mixin Mixin {}

class Base {
  const Base();
}

class Sub = Base with Mixin;

void main() {
  const Sub();
}

@srawlins, @scheglov, please reopen the issue or create a new one if you disagree.