Replace JSONPath with jq in jsondocck

[fluiderson]

This is an ongoing effort to close #142479. I've decided to take a hard path and rewrite rustdoc-types's entire testsuite. I don't think it'll be a good idea to construct a JSONPath-jq transpiler because it'll look really awkward for new contributors, JSONPath's limitations + jaq's own quirks may create a lot of questions that even current maintainers would've no answers for without digging into jsondocck's internals.

I expect jsondocck to have just 2 directives: jq and arg. Thanks to jq's flexibility, these 2 can do everything that the current directive set can and much more (actually, too much, I left some comments to opt out some dependencies when it'll be possible on jaq's side). I'm trying to actively utilize jq's features instead of just blindly rewriting existing assertions, so there should be more deletions than additions.

When I'll be done, I'll try to rebase and split my work to make it more easier to review. So far jsondocck is already functional, so you can check out how it may look like and give some feedback if you want. I'll commit updated tests folder by folder.

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Build completed unsuccessfully in 0:01:14
  local time: Fri Jun 27 11:49:53 UTC 2025
  network time: Fri, 27 Jun 2025 11:49:54 GMT
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