No string completions for indexed access types

[DanielRosenwasser]

interface Foo {
    hello: number;
    world: string;
}

let x: Foo['']

Try to request completions within the string literal.

Expected: completions for hello and world
Actual: no completions

[DanielRosenwasser]

@mariusschulz, you said you might be interested in working on this?

[Kingwl]

i'd like to working on this😂

[DanielRosenwasser]

Sorry, @mariusschulz DM'd me on Twitter. You've been doing an awesome job with the PRs though @Kingwl!