IDL Gen: Support Function/Method Overloading

[nikeokoronkwo]

The current IDL generator does not support overloading of interface methods. This issue is to add support for method overloading (similar to how it's currently being done in the Dart interface interop generator).

interface MyMethodExamples {
  void update(DOMString key, DOMString value);
  void update(sequence<DOMString> keys);
};