bug#60691: 29.0.60; Slow tree-sitter font-lock in ruby-ts-mode

[Juri Linkov <juri@linkov.net>]

X-Debbugs-Cc: Dmitry Gutov <dgutov@yandex.ru>

After more rules were added recently to ruby-ts--font-lock-settings,
font-lock became slow even on very small files.  Some measurements:

M-: (benchmark-run 1000 (progn (font-lock-mode -1) (font-lock-mode 1) (font-lock-ensure)))

M-x ruby-mode
(1.3564674989999999 0 0.0)

M-x ruby-ts-mode
(8.349582391999999 2 6.489918534000001)

This is not a problem when files are visited infrequently, but
becomes a problem for diff-syntax fontification that wants to
highlight simultaneously many files from git logs.
So a temporary measure would be not to enable ruby-ts-mode
in internal buffers:

(add-hook 'find-file-hook
          (lambda ()
            (when (and (eq major-mode 'ruby-mode)
                       ;; Only when not internal as from diff-syntax
                       (not (string-prefix-p " " (buffer-name))))
              (ruby-ts-mode))))