Add test for lambda parameter named 'readonly'

Author: Andy Hanson

tests/baselines/reference/readonlyInNonPropertyParameters.errors.txt

@@ -16,4 +16,6 @@ tests/cases/compiler/readonlyInNonPropertyParameters.ts(7,2): error TS2369: A pa
     }
     (readonly x) => 0;
      ~~~~~~~~~~
-!!! error TS2369: A parameter property is only allowed in a constructor implementation.
+!!! error TS2369: A parameter property is only allowed in a constructor implementation.
+    // OK to use `readonly` as a name
+    (readonly) => 0;

tests/baselines/reference/readonlyInNonPropertyParameters.js

@@ -5,7 +5,9 @@ class X {
 	method(readonly x: number) {}
 	set x(readonly value: number) {}
 }
-(readonly x) => 0;
+(readonly x) => 0;
+// OK to use `readonly` as a name
+(readonly) => 0;
 
 //// [readonlyInNonPropertyParameters.js]
 // `readonly` won't work outside of property parameters
@@ -21,3 +23,5 @@ var X = (function () {
     return X;
 }());
 (function (x) { return 0; });
+// OK to use `readonly` as a name
+(function (readonly) { return 0; });

tests/cases/compiler/readonlyInNonPropertyParameters.ts

@@ -5,4 +5,6 @@ class X {
 	method(readonly x: number) {}
 	set x(readonly value: number) {}
 }
-(readonly x) => 0;
+(readonly x) => 0;
+// OK to use `readonly` as a name
+(readonly) => 0;