json: switch to yyjson

[allomanta]

This should update the plugins relying on json to match the switch to yyjson from the wayfire master branch. I also have changes for the filters submodule locally, but I can't figure out how to include them.
I called the variables for the optionals maybe_x and maybe_y, but maybe there's a nicer way to fix this.

[soreau]

Overall your patch seems pretty straightforward. To pass CI, you will need to change json packages as in this commit and apply the diff from the uncrustify check. Aside from minor changes needed, it looks good to me. 👍

[allomanta]

I think uncrustify should be happy with the style now. I haven't been able to run it myself, but it seems like it just wanted the = signs to align. I also changed the json package in the CI, so that should work now I think.

[soreau]

Thanks!