bug#73404: 30.0.50; [forward/kill/etc]-sexp commands do not behave as expected in tree-sitter modes

[Juri Linkov]

>> This patch keep the current function treesit-forward-sexp,
>> and creates a new function treesit-forward-sexp-list
>> that uses the 'sexp-list' thing to navigate lists while
>> using forward-sexp-default-function to navigate atoms:
>
> Introducing a new command raises the question how should users
> navigate using the two.  Will C-M-<RIGHT> invoke forward-sexp or the
> new command (or maybe one or the other in some dwin-ish way)?
>
> What are the problems with teaching treesit-forward-sexp do what the
> new command does?  IOW, why do we need a new command?

Actually, it's not a new command, but a new function for C-M-<RIGHT>
via forward-sexp-function.  This is from treesit-major-mode-setup:

  (when (treesit-thing-defined-p 'sexp nil)
    (setq-local forward-sexp-function #'treesit-forward-sexp)
    (setq-local transpose-sexps-function #'treesit-transpose-sexps))

  (when (treesit-thing-defined-p 'sexp-list nil)
    (setq-local forward-sexp-function #'treesit-forward-sexp-list))

When a ts-mode defines the 'sexp-list' thing, only then it's used.
Otherwise the current implementation with 'sexp' is used for C-M-<RIGHT>.