fix(injector): allow multiple loading of function modules

move the loadedModules lookup to be performed only on strings in order to allow loading functions that look the same. this issue caused only the first `angular.mock.module(object)` invocation to work since the loadModules lookup blocked all following invocations.

closes #7254
I don't think it's very good to give the hashMap its own "unique uid" without removing the hashKey from module functions / objects, though, because this will reset every time the injector is created (assuming the injector has an isolate uid), and it becomes possible for moduleFns to have duplicate uids and not be called