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 moved it into a function since it is used in three places (Angular.js, testabilityPatch.js and now also apis.js) and I don't want all of them to have to know that the initial uid is ['0', '0', '0']