Clarify documentation for paginator jmespath

In this part of the docs, there's an example of using jmespath with a paginator.

I'm not an expert in JMESPath, but isn't "Contents[?Size > `100`][]" the same as "Contents[?Size > `100`]"? I tried both and they give the same results. So should we simplify this?

I think it would also be beneficial to state how to do this without any filtering. i.e. "Contents[]" (as opposed to * or . or something else a new user may guess.) (Or if there's another way of flattening without filtering, like .build_full_result() but as a generator not in-memory list, document that instead.)

And I think it would be beneficial to point out that the string Contents is specific to the API call. It's not usable for other paginators.