Refactored tests using Array constructor:

Some moved to tests with stdlib
Some changed to use arrayOfNulls

compiler/testData/codegen/boxWithStdlib/multiDeclForArray/MultiDeclForComponentExtensions.kt

@@ -0,0 +1,19 @@
+class C(val i: Int) {
+}
+
+fun C.component1() = i + 1
+fun C.component2() = i + 2
+
+fun doTest(l : Array<C>): String {
+    var s = ""
+    for ((a, b) in l) {
+      s += "$a:$b;"
+    }
+    return s
+}
+
+fun box(): String {
+  val l = Array<C>(3, {x -> C(x)})
+  val s = doTest(l)
+  return if (s == "1:2;2:3;3:4;") "OK" else "fail: $s"
+}