Improve tree-sitter imenu for c-mode and js-mode

Improve tree-sitter imenu for c-mode and js-mode

Instead of a flat list, now categorize imenu entries into categories
like "Function", "Variable", "Class", etc.

* lisp/progmodes/c-ts-mode.el (c-ts-mode--imenu-1): Handle more edge
cases.
(c-ts-mode--imenu): Categorize menu entries.
* lisp/progmodes/js.el (js--treesit-imenu-type-alist): Remove variable.
(js--treesit-imenu-label): Remove function.
(js--treesit-imenu-1): Use the name alone for labels.
(js--treesit-imenu): Categorize menu entries.