Allow `TokenFilter`s to keep empty arrays and objects

[nik9000]

Include version information for Jackson version you use: We use 2.10.4 but 2.13 doesn't support this either

Maybe this is possible in a way I don't know about, but I was hoping I could write a TokenFilter that could preserve empty arrays and objects. It looks like now if a TokenFilter#includeProperty doesn't return INCLUDE_ALL for an empty array then the array is removed. I'd love it if the TokenFilter could make that choice- maybe something like adding this to TokenFilter:

    public boolean includeEmptyArray(boolean contentsFiltered) throws IOException {
        return false;
    }

There is already a filterFinishArray but I don't think I can control the underlying filter with it. And I'm not sure if I can tell if the filter has filtered the contents of the array or not.

[nik9000]

Something like this seems to work, but I really don't know the code base so i can't be sure it makes sense.

I see INCLUDE_NON_NULL which is new to me but I don't think it does what I want. It looks like it preserves the path to filtered stuff and I don't want that.

[cowtowncoder]

One quick note: is this related to/same as #708 ? If so I wish I had time to work on it; help would be appreciated.
Although time-wise might be getting too late to address for 2.13.

[nik9000]

is this related to/same as #708 ?

I had another look this morning and I think so. I'll try and open up a PR soon. I think the code that I linked in the gist works fine for the builder side. Filtering the parsers are a little wow. I'll keep poking at it. There's a whole giant switch statement I haven't looked at yet.

[cowtowncoder]

Yes, the code is.... scary. It violates my usual "never write as clever code as you can since the person debugging code must be twice as clever as the person who wrote it (hence write only half as clever you could)".