Fix for incorrect behaviour for ruby block split/join

It fixes following corner cases:

* block without surrounding spaces
* block prepended by `#method?`, `#method!` lambda `->` definition


The name `bloc_replace` doesn't seem right to me. Usually, I'd call it "replacement", because that's its purpose here, but that's already taken by something else...

How about we name it `multiline_block`? Arguably, that's also its nature, looked at from a different angle.