[NI] Fix not-null smartcast on intersection of nullable types

#KT-28670 Fixed

compiler/testData/diagnostics/tests/generics/nullability/notNullSmartcastOnIntersectionOfNullables.kt

@@ -0,0 +1,18 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+interface A
+interface B {
+    fun test() {}
+}
+
+fun <K> select(a: K, b: K): K = a
+
+fun test(a: A?, b: B?) {
+    b as A?
+    a as B?
+    val c = select(a, b)
+    if (c != null) {
+        <!DEBUG_INFO_SMARTCAST!>c<!>.test()
+    }
+}

compiler/testData/diagnostics/tests/generics/nullability/notNullSmartcastOnIntersectionOfNullables.txt

@@ -0,0 +1,17 @@
+package
+
+public fun </*0*/ K> select(/*0*/ a: K, /*1*/ b: K): K
+public fun test(/*0*/ a: A?, /*1*/ b: B?): kotlin.Unit
+
+public interface A {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public interface B {
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open fun test(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}