Add 'treesit-sexp-thing' to use instead of 'treesit-sexp-type-regexp'.

Add 'treesit-sexp-thing' to use instead of 'treesit-sexp-type-regexp'.

* lisp/treesit.el (treesit-sexp-thing): New variable to use
instead of 'treesit-sexp-type-regexp'.
(treesit-sexp-thing-down-list): Rename from 'treesit-sexp-type-down-list'.
(treesit-sexp-thing-up-list): Rename from 'treesit-sexp-type-up-list'.
(treesit-forward-sexp, treesit--forward-list-with-default)
(treesit-down-list, treesit-up-list): Update references to the
above variables.
(treesit-cycle-sexp-thing): Rename from 'treesit-cycle-sexp-type'.

* lisp/progmodes/elixir-ts-mode.el (elixir-ts-mode): Update same variables.

* lisp/progmodes/heex-ts-mode.el (heex-ts-mode): Set these variables
instead of calling the function that sets them.

* lisp/progmodes/python.el (python-ts-mode): Check if variables
'treesit-sentence-type-regexp' and 'treesit-sexp-type-regexp' are bound.

https://lists.gnu.org/archive/html/emacs-devel/2025-06/msg00182.html
(cherry picked from commit 76f422da26b09a5d2646c0597871423f019a9573)