Avoid confusing TS9025 error in isolatedDeclarations

[Andarist]

fixes #60123

[jakebailey]

I think this is okay; erroring code will emit an error elsewhere, so letting declaredParameterTypeContainsUndefined "lie" a little to prevent follow-ons feels fine.

[jakebailey]

And in the case like:

// @ts-ignore
import { DoesNotExist } from "foo";

export class Bar {
    constructor(private x?: DoesNotExist | undefined) {}
}

The "worst thing" that happens here is that | undefined is spuriously left behind. Probably that's worth a test?

[jakebailey]

Ah, you already have that as a test via Unresolved.

[jakebailey]

Suggested change

	export function test2(x?: Unresolved | undefined): void {}
	export function test2(x?: Unresolved | undefined): void {}
	export function test3(x?: Unresolved): void {}

Maybe this extra test would be valuable?

[Andarist]

sure, i just pushed it out