jei_hides: use .concat instead of array-spread (Rhino compat). 0.21.0 -> 0.21.1.

KubeJS uses Rhino as its JS engine, which doesn't support array-spread
syntax (`[...a, ...b]`). The line `[...WAYSTONE_ITEMS, ...COIN_ITEMS]
.forEach(...)` threw EvaluatorException: syntax error at jei_hides.js:46
on client launch, surfacing the KubeJS client script errors dialog.

Fix: use Array.prototype.concat() which is universal JS. Also extracted
the hide-quietly helper into a named function for readability.

pack/overrides/kubejs/client_scripts/jei_hides.js

@@ -42,12 +42,17 @@ const COIN_ITEMS = [
     'numismatics:sun',
 ];
 
+// Some IDs may not exist (e.g. base 'waystones:sharestone' isn't
+// registered if only colored variants are). Swallow per-item failures
+// so one bad id doesn't break the whole pass.
+function hideQuietly(event, id) {
+    try { event.hide(id); } catch (e) {}
+}
+
 JEIEvents.hideItems(event => {
-    [...WAYSTONE_ITEMS, ...COIN_ITEMS].forEach(id => {
-        try { event.hide(id); } catch (e) {
-            // Some IDs may not exist (e.g. base 'waystones:sharestone' isn't
-            // registered if only colored variants are). Swallow per-item
-            // failures so one bad id doesn't break the whole pass.
-        }
+    // KubeJS uses Rhino, which doesn't support array-spread syntax
+    // (`[...a, ...b]`). Use .concat() for cross-engine safety.
+    WAYSTONE_ITEMS.concat(COIN_ITEMS).forEach(function(id) {
+        hideQuietly(event, id);
     });
 });