Replace JSONEditor library with svelte-jsoneditor

Could it be optional dependency?

Never mind. I found "Attach library" formatter option.

Actually implementing this is probably going to be a bit tricky. I've had an initial look at it and it's complicated by the library only being available in ESM form, both in Svelte and Vanilla forms. An initial pass with Webpack didn't get anywhere in being able to use it as an external lib. You could do it by baking the library in, but that'd blow out the size of the module.

I installed this on my site and, after disabling the Content Security Policy module, got the basic functionality working.

However, src/JsonFieldRequirements.php is still searching for yesmeck, which was removed from the README. Is jquery-jsonview also supposed to be removed by this MR? If so, JsonFieldRequirements.php needs to be updated, and if not, then the info on jsonview needs to be put back in the README.