Fix issue with ambient property declaration following property assignment in JS

[DanielRosenwasser]

Everyone is trying to fix #51521, so I guess I am too.

This PR tries to fix #51521. It does so by fixing setValueDeclaration to defer to property declarations over "assignment declarations" - even in the case of ambients. In the case of code like in the following .js file:

class C {
  constructor() {
    this.foo = 10;
  }
  declare foo: number;
}

We'll encounter the this.foo = 10 assignment first, then encounter declare foo: number;.

Even though declare foo: number is marked as ambient, it is arguably a better value declaration than the JavaScript one.

[DanielRosenwasser]

Wait. This is wrong.

[DanielRosenwasser]

The fact that the errors don't come up consistently, and that baselining doesn't give the same error results, is very suspicious.

[jakebailey]

Yeah. All tests I've had for this have not been compiler tests.

[Andarist]

Everyone is trying to fix #51521, so I guess I am too.

And now I have FOMO...

[DanielRosenwasser]

I am sure you can find something that looks broken with our JavaScript support.

[DanielRosenwasser]

Looks like @a-tarasyuk's PR makes a fix in the same place.