Support @value object stored in a class-named attribute.

[proofit404]

If @value decorated function returns a class, it should be stored in a class-named attribute.

If @value decorated function stored in a class-named attribute, it should return a class.

Followup of the https://github.com/proofit404/dependencies/issues/454#issuecomment-776922041

[proofit404]

Unfortunately, this can't be easily implemented before https://github.com/proofit404/dependencies/pull/382 will be merged.

We need name of the attribute available in the factory/builder function.

This was done in the major (not yet finished) refactoring we did to pass xenon check.