[analysis_server] Extract method should not extract expressions in a constant context.

[kallentu]

Currently, we allow extracting an expression when it's in a constant context, but that creates code that doesn't run (since we don't support constant functions).

For example:

enum E {
  v;
  void foo() {
    const e = E.v; // We extract E.v into a method using the extract method refactor
  }
}

Applies the refactoring to produce:

enum E {
  v;
  void foo() {
    const e = res(); // ERROR
  }

  E res() => E.v;
}

We should disallow the refactoring if we find that the expression is in a const context.

[FMorschel]

We should probably make sure that the create method/function/getter fixes don't do that, too, right? If you say:

enum E {
  v;

  void foo() {
    const _ = res();
    const _ = res;
  }
}

They should not show up.

[FMorschel]

Also similar to #61150.

[bwilkerson]

I agree. It seems wrong to offer a refactoring that will create invalid code, and I think we should disable the refactoring in that situation.

I say that mostly because we can't have a dialog with the user. In some ways the ideal might be to offer the refactoring, then tell the user that we can do what they asked for, but that it will produce invalid code because a method can't be invoked in a const context. We could suggest that we could remove the const as part of the refactoring, or we could leave it and they could fix the bug on their own. Unfortunately, we can't have such a conversation. (Though AI's can have a conversation, so maybe there's a path forward there someday.)