Preserve arity for preserving js optional parameters

[weswigham]

Fixes #36507

For relationship checking, we consider untyped signatures from js as only having 0 required arguments; however we also use that minimum argument count for calculating weather an initialized optional parameter is optional or not. In the later case, we would like that "js signatures have 0 required arguments" rule to not apply, so we can actually recover what parameters are optional.

[sandersn]

I believe this property also causes differences from TS when choosing overloads too. I'll need to read the change to see whether it might fix those too.

[sandersn]

Let me track down the overload bug so you can check whether it fixes that too. I think it probably will.

[sandersn]

#31888

With small repro:

/** @param {{
    (fn: (a: number) => void): number;
    (fn: (a: number, b: number) => void): string
}} id */
export function test(id) {
    /** @type {string} */
    var val = id((a, b) => a + b);
}

[sandersn]

The problems that my simple fix at #35153 had shows that we should look at webpack (and maybe some others?) before merging to see if they break with this.

[weswigham]

Let me track down the overload bug so you can check whether it fixes that too. I think it probably will.

It does not~
Behavior for actual call resolution is unchanged.