New command 'treesit-toggle-sexp-mode' (bug#76676).

New command 'treesit-toggle-sexp-mode' (bug#76676).

* lisp/treesit.el (treesit-forward-sexp): Don't use
'treesit-sexp-type-regexp' reserved for list commands
to override their default 'list' thing.
(treesit-down-list, treesit-up-list): Use
'treesit-sexp-type-regexp' instead of 'list'
when it's non-nil.
(treesit-toggle-sexp-mode): New command.

* lisp/progmodes/c-ts-mode.el (c-ts-mode--thing-settings):
Improve 'sexp' thing settings to exclude the top-level
"translation_unit" that just moves to EOF and also "comment".

* lisp/progmodes/elixir-ts-mode.el (elixir-ts--sexp-regexp): Remove.
(elixir-ts--forward-sexp): Remove to use the default 'sexp' navigation.
(elixir-ts--with-parens-0-p, elixir-ts--with-parens-1-p):
New internal functions.
(elixir-ts-mode): Add 'treesit-thing-settings'
instead of 'forward-sexp-function' (bug#76788).

* lisp/progmodes/heex-ts-mode.el (heex-ts--sexp-regexp): Remove.
(heex-ts--forward-sexp): Remove to use the default 'sexp' navigation.
(heex-ts--thing-settings): New variable.
(heex-ts-mode): Use 'heex-ts--thing-settings'
instead of 'forward-sexp-function'.

* lisp/progmodes/java-ts-mode.el (java-ts-mode):
Improve 'sexp' thing to use settings like in c-ts-mode.

* lisp/progmodes/php-ts-mode.el (php-ts-mode):
Improve 'sexp' thing settings to exclude the top-level
"program" that just moves to EOF and also "comment".

* lisp/progmodes/ruby-ts-mode.el (ruby-ts-mode):
Improve 'sexp' thing to use settings like in c-ts-mode.

* lisp/textmodes/css-mode.el (css--treesit-thing-settings):
Add 'sexp' thing.  Add "string_value" to 'text' thing.

* lisp/textmodes/html-ts-mode.el (html-ts-mode--treesit-things-settings):
Improve 'sexp' thing to use settings like in c-ts-mode.
Add "doctype" to the 'list' thing.

(cherry picked from commit 99a2cb05a41c66565d417e11e60f4324aaa5c5b5)