Allow keyword argument for Object#enum_for

[ksss]

Example

enum_for(:instance_exec, x: 123){ |x:| p x}.size
#=> 123

Real case

lib/rbs/file_finder.rb:8:13: [error] Cannot find compatible overloading of method `enum_for` of type `singleton(::RBS::FileFinder)`
│ Method types:
│   def enum_for: (::Symbol, *untyped) ?{ (*untyped) -> ::Integer } -> ::Enumerator[untyped, untyped]
│               | () ?{ () -> ::Integer } -> ::Enumerator[untyped, self]
│
│ Diagnostic ID: Ruby::UnresolvedOverloading
│
└       return enum_for(__method__, path, immediate: immediate, skip_hidden: skip_hidden) unless block
               ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[soutaro]

🙏