Support treesit-defun-name in tree-sitter major modes

Support treesit-defun-name in tree-sitter major modes

* lisp/progmodes/csharp-mode.el (csharp-ts-mode--defun-name): New
function.
(csharp-ts-mode--imenu-1): Extract into new function.
(csharp-ts-mode): Setup treesit-defun-name-function.
* lisp/progmodes/java-ts-mode.el (java-ts-mode--defun-name): New
function.
(java-ts-mode--imenu-1): Extract into new function.
(java-ts-mode): Setup treesit-defun-name-function.
* lisp/progmodes/js.el (js-treesit-current-defun): Remove function.
This function is not used (for a while already).
(js--treesit-defun-name): New function.
(js--treesit-imenu-1): Extract into new function.
(js-ts-mode): Setup treesit-defun-name-function.
* lisp/progmodes/json-ts-mode.el (json-ts-mode--defun-name): New
function.
(json-ts-mode--imenu-1): Extract into new function.
(json-ts-mode): Setup treesit-defun-name-function.
* lisp/progmodes/python.el (python--treesit-defun-name): New function.
(python--imenu-treesit-create-index-1): Extract into new function.
(python-ts-mode): Setup treesit-defun-name-function.
* lisp/progmodes/rust-ts-mode.el (rust-ts-mode--defun-name): New
function.
(rust-ts-mode--imenu-1): Extract into new function.
(rust-ts-mode): Setup treesit-defun-name-function.
* lisp/textmodes/css-mode.el (css--treesit-defun-name): New function.
(css--treesit-imenu-1): Extract into new function.
(css-ts-mode): Setup treesit-defun-name-function.
* lisp/textmodes/toml-ts-mode.el (toml-ts-mode--get-table-name):
Remove function.
(toml-ts-mode--defun-name): New function.
(toml-ts-mode--imenu-1): Extract into new function.
(toml-ts-mode): Setup treesit-defun-name-function.