Support sealed class inheritors in the same file

#KT-11573 Fixed

compiler/testData/codegen/box/classes/sealedInSameFile.kt

@@ -0,0 +1,38 @@
+class B : A()
+
+sealed class A() {
+    constructor(i: Int): this()
+
+    class C: A()
+}
+
+object T : Y()
+
+class D : A(4)
+
+class E : A {
+    constructor(i: Int): super(i)
+    constructor(): super()
+}
+
+object S : Z()
+
+sealed class Y : X()
+
+sealed class Z : Y()
+
+sealed class X : A()
+
+class Q : Y()
+
+fun box() : String {
+    B()
+    A.C()
+    D()
+    E()
+    E(4)
+    T
+    S
+    Q()
+    return "OK"
+}