Rework tree-sitter font-lock

Rework tree-sitter font-lock

Remove :toggle and :level, add :feature.

* lisp/progmodes/js.el (js--treesit-settings): Add :feature.
(js--treesit-enable): Set treesit-font-lock-feature-list.
* lisp/progmodes/python.el: Replace :level with :feature.
(python-mode): Set treesit-font-lock-feature-list.
* lisp/treesit.el (treesit-font-lock-feature-list): New variable.
(treesit-font-lock-settings): Change format.
(treesit-font-lock-rules): Remove :toggle and :level, add :feature.
(treesit-font-lock-recompute-features): New function.
(treesit-font-lock-fontify-region): Change to work with the new
format.
(treesit-font-lock-enable): Add call to
treesit-font-lock-recompute-features.  And improve the font-lock-mode
workaround.