Extract Function: Support multi-declaration initializers

#KT-5613 Fixed

idea/testData/refactoring/extractFunction/initializers/properties/multiDeclaration.kt

@@ -0,0 +1,7 @@
+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) = <selection>1 to 2</selection>
+}

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

@@ -0,0 +1,11 @@
+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) = pair()
+}
+
+private fun pair(): Pair<Int, Int> {
+    return 1 to 2
+}

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

@@ -0,0 +1,13 @@
+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) {
+                <selection>1 + 1</selection>
+                1 to 2
+            } else {
+                2 to 3
+            }
+}

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
+}