Small fix: encode index of ArrayIndex operation as constant operand

Author: DSouzaM

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/compiler/bytecode_dsl/RootNodeCompiler.java

@@ -3707,9 +3707,8 @@ private void patternHelperSequenceUnpack(PatternTy[] patterns, PatternContext pc
 
             for (int i = 0; i < n; i++) {
                 b.beginStoreLocal(pc.subject);
-                b.beginArrayIndex();
+                b.beginArrayIndex(i);
                 b.emitLoadLocal(unpacked);
-                b.emitLoadConstant(i);
                 b.endArrayIndex();
                 b.endStoreLocal();
 

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/bytecode_dsl/PBytecodeDSLRootNode.java

@@ -892,9 +892,10 @@ public Object readSelf(Frame frame) {
     }
 
     @Operation
+    @ConstantOperand(type = int.class)
     public static final class ArrayIndex {
         @Specialization
-        public static Object doObject(Object[] array, int i) {
+        public static Object doObject(int i, Object[] array) {
             return array[i];
         }
     }