Add helper constants for nonmutating method names

[fatkodima]

For context https://github.com/rubocop-hq/rubocop-performance/pull/140/files#r439732580

Bullet number 4

and those ENUMERABLE_METHOD_NAMES, NONMUTATING_ARRAY_METHODS and NONMUTATING_HASH_METHODS into rubocop-asts AST::CollectionNode module?

But it is not really belongs to rubocop-ast, I was wrong. So opened pr here.

[marcandre]

it is not really belongs to rubocop-ast, I was wrong.

Why? IMO all criteria that are independent of a particular cop, that can be factually said to be accurate outside of a context, should be in rubocop-ast, these included.

[fatkodima]

Ok. So is this file a good place for those constants https://github.com/rubocop-hq/rubocop-ast/blob/master/lib/rubocop/ast/node/mixin/method_identifier_predicates.rb ?
And if so, should I also add pedicate methods like nonmutable_array_method?, etc there?

[marcandre]

I think so

[fatkodima]

Opened on rubocop-ast rubocop/rubocop-ast#38