Add outlining spans for 'type' declarations

[mjbvz]

From microsoft/vscode#95577

TypeScript Version: 3.9.0-dev.20200420

Search Terms:

• fold / folding
• outlining spans / getOutliningSpans
• type

Code
For the TS:

interface A {
    x: number
}

type B = {
    y: number
}

Expected behavior:

Both A and B are foldable

Actual behavior:

Only the interface (A) is foldable

[a-tarasyuk]

I noticed that Tuple type doesn't have outlining spans too,

type Foo = [
    number,
    number
]

@mjbvz Do you think it makes sense to add outlining spans for the Tuple type?

cc @DanielRosenwasser

[orta]

Yeah, I think we should 👍

[16oh4]

@orta @a-tarasyuk @mjbvz Cool, thanks a lot!