New treesit generic mode 'liquid-generic-ts-mode' (bug#77255)

New treesit generic mode 'liquid-generic-ts-mode' (bug#77255)

* lisp/treesit.el (treesit-replace-font-lock-feature-settings):
Check the query language in addition to checking the feature.
(treesit-font-lock-fontify-region): Use treesit-font-lock-setting-*
accessors.

* lisp/treesit-x.el (treesit-generic-mode-setup): Append new
font-lock rules to an existing treesit-font-lock-settings
possibly inherited from the parent.
(treesit-generic-mode-setup): Use treesit-merge-font-lock-feature-list
to merge with an existing feature list inherited from the parent.
(liquid-generic-ts-mode): New treesit generic mode.
(alpinejs-generic-ts-setup): New treesit generic setup.

(cherry picked from commit 87da719b6c4a53a31c67f3a9646b68cb15a1ffe7)