Make validators accept lambdas without record argument

[fatkodima]

Fixes #45117.

[jonathanhefner]

It looks like this pattern also occurs elsewhere:

• active_model/validations/length.rb
• active_model/validations/numericality.rb
• active_model/validations/format.rb
• active_model/validations/clusivity.rb

I feel like we should be consistent in what we support, so what do you think about factoring out a resolve_value(record, value) method? It could live in a ResolveValue module in active_model/validations/resolve_value.rb, which could be included where required.

(Alternatively, we could add it as a utility method to the Validator or EachValidator class, but that feels a little off.)

Note that in some cases we check value.respond_to?(:call) instead of Proc === value, so we would (unfortunately) probably have to check for both to avoid breaking existing code.

[fatkodima]

Ooh, I was sure that this is already supported in other places. Thanks for the suggestion, I will do that.

[fatkodima]

Updated.

[jonathanhefner]

Thank you, @fatkodima! 😄