chore(doc-gen): convert heritage for private constructor classes

When we are creating a type definition file for a class has a private constructor,
we convert it to a combination of an instance of a concrete type with no constructor and an interface that contains the other methods.

When this happens, we must also convert the class's heritage from
`implements` to `extends` since interfaces cannot implement other interfaces
or classes.

Fixes a problem with angular#2996
Closes angular#3002

docs/typescript-definition-package/processors/createTypeDefinitionFile.js

@@ -76,6 +76,11 @@ module.exports = function createTypeDefinitionFile(log) {
               // Convert this class to an interface with no constructor
               exportDoc.docType = 'interface';
               exportDoc.constructorDoc = null;
+
+              if (exportDoc.heritage) {
+                // convert the heritage since interfaces use `extends` not `implements`
+                exportDoc.heritage = exportDoc.heritage.replace('implements', 'extends');
+              }
 
               // Add the `declare var SomeClass extends InjectableReference` construct
               modDoc.doc.exports.push({