[ruby/prism] Implement on_op for ripper

Mostly the same as for `on_kw`.

Stop comparing order for a handful of events. They are emitted by ripper in a order that is
not easy for prism to replicate. For example in`foo, bar, baz = 123`, `op` for `=` is emitted
before the last mass assign identifier (so `foo`, `bar`, `=`, `baz`.

I don't want to replicate that if I don't have to. Same for `::` in `A::B = 123` etc.

ruby/prism@4d88aed5e9

Author: Earlopain