Filter undefined only in binding patterns in parameters w/initialiser

[sandersn]

#37309 removes undefined from the type of any binding pattern whose parent has an initialiser. But this is only correct when the initialiser is for a parameter. Here's a counter-example:

declare let x: { s: string } | undefined;
const { s } = x;

This PR removes undefined from the type of a binding pattern only when
the binding pattern's parent is a parameter. This fixes the regression
from 3.8. However, it's still not the ideal fix; we should be able to
use control flow to solve this problem. Consider:

const { s }: { s: string } | undefined = { s: 'hi' }
declare function f({ s }: { s: string } | undefined = { s: 'hi' }): void

Neither line should have an error, but the first does in 3.8 and after
this change.

Fixes #38110