Extract common optimizer tests (#52169)

Author: astefan

x-pack/plugin/ql/src/test/java/org/elasticsearch/xpack/ql/TestUtils.java

@@ -36,6 +36,10 @@ public static Configuration randomConfiguration(ZoneId zoneId) {
                 randomAlphaOfLength(10));
     }
 
+    public static Literal of(Object value) {
+        return of(Source.EMPTY, value);
+    }
+
     /**
      * Utility method for creating 'in-line' Literals (out of values instead of expressions).
      */