WIP fix for kw args issue - DO NOT MERGE

See https://github.com/rspec/rspec-mocks/pull/726
The fact that multiple things have to check `skip_kw_args?` is suggesting to me that we're missing a chance to use polymorphism instead.  WDYT about the idea of having a `LooseVerifier` (or `AllowsMatchersForKwArgsVerifier`, or whatever) subclass that has the extra `skip_kw_args` logic?  I think I prefer the API at the callsite of instantiating a different class rather than passing a flag, too...flags that toggle behavior are a bit of a code smell IMO, when there are alternatives like using different objects that implement the same interface with slightly different logic.