Allow to access exports from inside a commonjs module

[ghost]

Fixes #15809

Note: The following will no longer work as a constructor function:

exports.f = function() {
    this.x = 1;
}

because we expect that this will be exports, and we get a "property 'x' does not exist" error.

[rbuckton]

Note: The following will no longer work as a constructor function:

exports.f = function() {
   this.x = 1;
}

Do we think this will be an issue for adoption?

// CC: @DanielRosenwasser, @mhegazy, @bowdenk7

[ghost]

Bump @DanielRosenwasser, @mhegazy, @bowdenk7

[mhegazy]

Note: The following will no longer work as a constructor function:

I am not sure i understand the issue here.

[ghost]

Fixed the issue by changing getContextualThisParameterType to never contextually type this to the source file symbol.