feat: expose default value in hover

[Rafał Chłodnicki (rchl)]

I don't know if you are interested in such a feature and it's fine if not but I thought I'll try to upstream it instead of just having a local patch.

[Jon Surrell (sirreal)]

examples has the same gap:

{ "a": { "type": "string", "description": "D", "default": "dflt", "examples": ["ex1"] } }

Hovering "a" gives ["D"]. Both annotations are dropped, even though completion at the value position already proposes them ("dflt" with detail: "Default value", "ex1" with none).