feat(highlights)!: enforce documented captures (#6232)

Problem: Allowing undocumented "secret" (sub)captures makes it harder
to write comprehensive colorschemes and catch inconsistent captures.

Solution: Only allow captures listed in CONTRIBUTING.md. Add useful
(cross-language) subcaptures and drop language-specific or too niche
ones.

Follow-up: Adding further `*.builtin` captures and changing queries to
use them.

Language-specific subcaptures should instead be added in user config or
a custom language plugin.

queries/jsonnet/highlights.scm

@@ -118,7 +118,7 @@
   identifier: (id) @variable.parameter)
 
 (bind
-  (id) @variable.local)
+  (id) @variable)
 
 (bind
   function: (id) @function)