Complete the iterator interface

[ChrisRackauckas]

The iterator interface for NonlinearSolve.jl was never completed in the past, but it's very close. Next steps are:

• [ ] add dispatches for the common solve step! interface
• [ ] Setup the abstract caches as iterators that automatically iterate, and test with for loops
• [ ] Update the iterator interface page to showcase some uses, like in for loops https://docs.sciml.ai/NonlinearSolve/stable/tutorials/iterator_interface/

As inspiration, see https://docs.sciml.ai/DiffEqDocs/stable/basics/integrator/

[avik-pal]

This was done with 3.5 release