JVM_IR optimize temporary vals initialized with other vals

compiler/testData/codegen/bytecodeText/temporaryVals/arrayCompoundAssignment.kt

@@ -0,0 +1,9 @@
+fun test(xs: IntArray, dx: Int) {
+    for (i in xs.indices) {
+        xs[i] += dx
+    }
+}
+
+// JVM_IR_TEMPLATES
+// 5 ALOAD
+// 6 ILOAD