Support completions in destructuring in for-of

[ghost]

Fixes #16452

@rbuckton I wanted to test this with for-await-of but couldn't seem to get it to work.
I tried:

// @lib: esnext

////...existing test...
////async function f(points: AsyncIterable<{ x: number, y: number }>) {
////    for await (const { /*d*/ } of points) {}
////}
verify.noErrors();

I get: minChar: 173, limChar: 186, message: Cannot find name 'AsyncIterable'.

[mhegazy]

@Andy-MS the error indicates the lib is not loaded correctly. is this a test-only issue or you see it with VSCode as well?

[ghost]

Test-only.

[mhegazy]

We need to look into why fourslash is not including the library correctly.