core: Array#include? and Enumerable#include? should take non-Elem types

[tk0miya]

For example, Array[Integer] can take other number types validly:

> [1, 2, 3].include? 2.0
=> true
> [1, 2, 3].include? Complex(2)
=> true
> [1, 2, 3].include? Rational(2)
=> true

refs: soutaro/steep#1482

[ksss]

In reality, it seems that the == method is being used as an interface.

irb(main):005> TracePoint.new(:a_call) { |tp| p tp }.enable { [1, 2, 3].include? 2.0 }
#<TracePoint:b_call (irb):5>
#<TracePoint:c_call 'include?' (irb):5>
#<TracePoint:c_call '==' (irb):5>
#<TracePoint:c_call '==' (irb):5>
=> true

However, since == is a method of BasicObject, it applies to almost all objects.
Therefore, using untyped is fine.

[tk0miya]

Initially, I thought to allow taking nil value. Therefore I changed this type as follows once:

Suggested change

	def include?: (untyped object) -> bool
	def include?: (Elem? object) -> bool
	| (untyped object) -> false

But I noticed it does not help the numbers' case. Therefore, I used untyped here finally.

[soutaro]

I prefer keeping the strict method type, because finding a code passing an unexpected object to include? actually helps.

Can you share the code where you want this? @tk0miya

[soutaro]

Ah, soutaro/steep#1482...

%w,true,.include?(ENV['foo'])

Hmm...

[soutaro]

No conclusion yet, though I'm not very positive about this change.
Skipped in 3.9.