Make setter accept undefined

[sweet lily]

That's not what I'm seeing in the playground....

[sleek abyss]

Gerrit0#7591

Playground Link

Preview:```ts
class Data {
private _test = ""

get test(): string {
return this._test
}
set test(v: string | undefined) {
if (v !== undefined) {
this._test = v
}
}
}

const x = new Data()
x.test = "a"
x.test = undefined
...```

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[balmy mulch]

Finally found the issue, it happens when the type is coming from an interface like so:
I ignored that while making an example code

[sleek abyss]

AlexanderX#3054

Playground Link

Preview:```ts
interface iface {
member?: string
}

class Data {
private _test = ""

get test(): iface["member"] {
return this._test
}
set test(v: iface["member"]) {
if (v !== undefined) {
this._test = v
}
}
}
...```

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[balmy mulch]

And I forgot | undefined here, though the member? does the same thing. This is not the case in my code, huh?!

I'm so confused

Now, whole the issue is gone magically, even this (copy-paste) is not erroring in vscode, which is also basically the same with my original code.
this is playground

[sleek abyss]

AlexanderX#3054

Playground Link

Preview:```ts
class Data {
get test(): number {
return 1
}
set test(v) {}
}

let d = new Data()
d.test = undefined
Math.ceil(d.test)```

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[balmy mulch]

and this is a ts file with 0 errors in vscode

I was already expecting it to accept undefined by default for any type, here it randomly worked properly.

Ok it seems the inconsistency in my local is because I was testing the original TS class from a JS file with @ts-check