Retain data flow info after multi-declaration

#KT-2825 In Progress

compiler/testData/diagnostics/tests/dataFlowInfoTraversal/MultiDeclaration.kt

@@ -0,0 +1,7 @@
+fun Int.component1() = "a"
+
+fun foo(a: Number) {
+    val (x) = a as Int
+    a : Int
+    x : String
+}