RST: update parser and queries

- The directive type does not longer includes `::`.
- The content of the directives is not longer interpreted as rst,
  but it uses language injection for it.
- Fix a query to allow to capture targets without link.
- Reset the content of the math role so it can be highlighted by the
  injection instead.

Problems I found:

- Capturing the same node with @language and @content will raise an
  error.

  ```
  Error detected while processing FileType Autocommands for "*":
  E5108: Error executing lua /usr/share/nvim/runtime/lua/vim/treesitter/languagetree.lua:331: table index is nil
  ```

  Harcoding the language works, Using the offset predicate doesn't work
  either `(#offset! 0 0 1 0)` nor `(#offset! 0 0 0 5)`

- Generating the grammar using `tree-sitter-cli@0.17.x` breaks
  nvim-treesitter, `@0.16.9` works.

lockfile.json

@@ -93,7 +93,7 @@
     "revision": "be2e415b5716615530234d179dc27c32b7a1d86b"
   },
   "rst": {
-    "revision": "aa61d0e2930de134089326973686ac547cca9e03"
+    "revision": "226196277df51e5222f3113a3c814dd8b17e70e7"
   },
   "ruby": {
     "revision": "bb572f60e9538bd11fbde95a54f97522073f1e06"