fix(loader): don't rely on internal APIs

This significantly increases the size of the loader:
- minified: 1031bytes -> 1509bytes (+46%)
- minified + gzip: 593bytes -> 810bytes (+36%)

I'm not entirely sold on the idea of shipping minErr with the loade. With the current state, the angular-loader behavior is completely broken - this is just a quick fix, we can revisit this change in the future.


Closes #4437
Closes #4874