Reduce class init time for Object model layouts.

Author: chumer

truffle/src/com.oracle.truffle.api.object/src/com/oracle/truffle/api/object/LayoutImpl.java

@@ -138,6 +138,12 @@ protected record Key(
                     int implicitCastFlags,
                     LayoutStrategy strategy) {
 
+        // letting Java generate hashcodes has slow startup
+        @Override
+        public int hashCode() {
+            return Objects.hash(type, implicitCastFlags, strategy);
+        }
+
         @Override
         public boolean equals(Object obj) {
             if (this == obj) {