Make treesit--simple-indent-eval more permissive (bug#78065)

* lisp/treesit.el (treesit--simple-indent-eval): Allow EXP to be
anything, so higher-order indent presets can take anything as an
argument: t, nil, symbols, keywords, etc.

lisp/treesit.el

@@ -1902,14 +1902,12 @@ the function."
         ;; `functionp'.
         ((alist-get exp treesit-simple-indent-presets))
         ((functionp exp) exp)
-        ((symbolp exp)
-         (if (null exp)
-             exp
-           ;; Matchers only return lambdas, anchors only return
-           ;; integer, so we should never see a variable.
-           (signal 'treesit-indent-error
-                   (list "Couldn't find the preset corresponding to expression"
-                         exp))))
+        ;; There are higher-order presets that take arguments, like
+        ;; (nth-sibling 1 t), so it's possible for exp to be something
+        ;; other than numbers and functions.  Don't signal an error if
+        ;; exp isn't a function nor a number.  In fact, allow exp to be
+        ;; any symbol or keyword, so users can define higher-order
+        ;; presets that takes keyword or symbol as arguments.
         (t exp)))
 
 ;; This variable might seem unnecessary: why split