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
option 1/ is the easiest and solves the current problem, but doesn't solve the issue of reusing an array of objects in tests that use repeaters. In that case you would still see the same kind of id conflict. (btw instead of a different range I would use a different counter).

We could implement it as a temporary solution and replace it with something better.