allow this in typeQuery

[Zzzen]

Fixes #1554

[sandersn]

Implementation looks good. One question about a test and a whole bunch of ideas for more tests.

We're close enough to the 4.3 release that I want to hold this one for 4.4.

[sandersn]

please add tests of

1. implicitly any usage, like function f() { let x: typeof this.no = 1 }. (x should have type any)
2. implicit any errors for the same code, but when noImplicitThis: true
3. The same usage in function f (this: { no: number })
4. usage inside arrow functions, to make sure that the emit is correct. It would be good to have an arrow function inside a container that binds this, like a class, and in one that doesn't, like a module.

[Zzzen]

Ooops, this type can not be used in plain functions. 🤷

    function Test1() {
        let x: typeof this.no = 1
                      ~~~~
!!! error TS2526: A 'this' type is available only in a non-static member of a class or interface.
    }
    

[sandersn]

That error is wrong, then, because this.no is an expression, not a type. The type would be like let x: this['no'].

[Zzzen]

I did not notice the differences between this type and this expression. Changing getThisType to checkThisExpression fixed it.

[sandersn]

does this work when the QualifiedName is nested, like this.x.y? I think you need a test for this.

[Zzzen]

It doesn't work for this.x.y. I've replaced isTypeQueryNode with isPartOfTypeQuery

[sandersn]

the QualifiedName case doesn't check that its ultimate parent is a TypeQuery, so I think you could maybe fool this with this.x in a weird location, or o.this.x The latter should be easy to add a test for; I don't know what test you need for the former.