Properly set Zeitwerk::NameError#name

[casperisfine]

Context: rails/rails#37650

TL;DR; vanilla NameError has a #name accessor that is useful to distinguish wether the constant we were trying to load is missing, or if the NameError is caused by some dependent code.

e.g. being able to tell the difference between:

# foo_controller.rb
class FoosControler # The expected constant doesn't exist
end

# foo_controller.rb
class FooControler
 ::DoesNotExist # Another constant resolution issue was triggered by loading foo_controlle.rb
end

What this patch does is to respect the NameError#name contract.

@fxn for review please.

cc @rafaelfranca @etiennebarrie @Edouard-chin

[fxn]

Thanks @casperisfine!

[fxn]

2.2.2 is out with this change.

[casperisfine]

❤️