Add a variable of type this in constructor body

The test already had a reference to the `this` value, but that doesn't
show that the *type* is allowed.

Author: sandersn

tests/baselines/reference/thisTypeErrors2.errors.txt

@@ -16,6 +16,7 @@ tests/cases/conformance/types/thisType/thisTypeErrors2.ts(9,38): error TS2526: A
         constructor(public host: Generic<this>) {
                                          ~~~~
 !!! error TS2526: A 'this' type is available only in a non-static member of a class or interface.
+            let self: this = this;
             this.n = 12;
         }
     }

tests/baselines/reference/thisTypeErrors2.js

@@ -8,6 +8,7 @@ class Generic<T> {
 class Derived {
     n: number;
     constructor(public host: Generic<this>) {
+        let self: this = this;
         this.n = 12;
     }
 }
@@ -27,6 +28,7 @@ var Generic = (function () {
 var Derived = (function () {
     function Derived(host) {
         this.host = host;
+        var self = this;
         this.n = 12;
     }
     return Derived;

tests/cases/conformance/types/thisType/thisTypeErrors2.ts

@@ -7,6 +7,7 @@ class Generic<T> {
 class Derived {
     n: number;
     constructor(public host: Generic<this>) {
+        let self: this = this;
         this.n = 12;
     }
 }