fix(:lang): add treesit-available-p checks to *-ts-mode packages

Otherwise package installation will throw Emacs version errors for users
on 28 and under.

modules/tools/tree-sitter/autoload/compat-30.el

@@ -7,6 +7,12 @@
 
 (autoload 'treesit-ready-p "treesit")
 
+;;;###autoload
+(unless (fboundp 'treesit-available-p)
+  (defun treesit-available-p ()
+    "Return non-nil if tree-sitter support is built-in and available."
+    nil))
+
 ;;;###autoload
 (defcustom treesit-auto-install-grammar 'ask
   "Whether to install tree-sitter language grammar libraries when needed.