It should be possible to get the error from the callback

**Is your feature request related to a problem? Please describe.**

I can't report the error to Sentry when loading the library fails.

**Describe the solution you'd like**

I'd like to be able to get the error from the `Loader` in the `Wrapper` `callback`.

**Describe alternatives you've considered**

There is a private `errors` property on the `Loader` but I do not want to rely on a private API.

**Additional context**

N/A