bug#66732: tree-sitter fontification doesn't update multi-line syntax reliably

[Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

> +(defun treesit--pre-redisplay (&rest _)
> +  (treesit-update-ranges)
> +  (dolist (parser (treesit-parser-list nil nil t))
> +    (treesit-parser-root-node parser)))

Note that `pre-redisplay-functions` is called often and can be called
N times for a single redisplay (if the buffer is displayed in
N windows), so we should try and make sure we only do the hard work if
there's actually been a change since the last time.

[ And the code should probably come with a comment explaining why
  calling `treesit-parser-root-node` and ignoring its return value is
  useful here.  ]

        Stefan