Add Hash#includes?(other : Hash) overload

[Sija]

This PR allows checking if a Hash includes given subset denoted by given other Hash.
Functionality asked for instance at SO - Ruby version.

Supersedes #7498 since it's a more versatile implementation, enhancing Hash API without a need for introducing special cases in ContainExpection matcher.

[j8r]

This doesn't closes #7497 ...
I'm not for or against this feature, at least I'm glad you understood https://github.com/crystal-lang/crystal/pull/7498/files#r261847933 – no need to have custom code related to Hash on the expectation anymore.

[asterite]

Ruby provides <, <=, > and >= for this (subset, subset or equals, superset, superset or equals). Let's do the same.

[dscottboggs]

I don't think it's accurate to say that this closes #7497. That issue was about a totally different question.

[Sija]

@asterite Cool, these are way better! How about also delegating Hash#includes?(other : Hash) to other <= self to allow contain expectation to work smoothly with it?

[straight-shoota]

#includes?(a) is defined as returning true when a is part of the collection. You're proposing an entirely different semantic, which is actually a subset predicate. This should be a different method and would be implemented by #7500.

I'd suggest to close this PR.

[straight-shoota]

I've given this some thought and maybe we could consider adding an overload Enumerable(T).includes?(collection : Enumerable) which returns true if all elements in collection are included in self. So that's essentially other.all? { |elem| includes?(elem) }.

/cc #7500 (comment)

[asterite]

If we do that it should be named includes_all?