Extract Function: Support multi-declaration initializers

#KT-5613 Fixed

idea/testData/refactoring/extractFunction/initializers/properties/nestedInMultiDeclaration.kt.after

@@ -0,0 +1,17 @@
+data class Pair<A, B>(val a: A, val b: B)
+fun <A, B> A.to(b: B) = Pair(this, b)
+
+// SIBLING:
+fun foo() {
+    val (a, b) =
+            if (true) {
+                unit()
+                1 to 2
+            } else {
+                2 to 3
+            }
+}
+
+private fun unit() {
+    1 + 1
+}