Put not-null original type as last possible smart cast target

This fixes muted tests testSmartCast (IDE highlighting) and
testNestedSealed (Diagnostics).
Together with commit 555b3f12 this makes #KT-15901 Fixed

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/smartcasts/DataFlowInfo.kt

@@ -46,6 +46,7 @@ interface DataFlowInfo {
      *
      * IMPORTANT: by default, the original (native) type for this value
      * are NOT included. So it's quite possible to get an empty set here.
+     * Also, type order in the result set MAKES SENSE so keep it stable and do not change without reason
      */
     fun getCollectedTypes(key: DataFlowValue): Set<KotlinType>
 
@@ -55,6 +56,7 @@ interface DataFlowInfo {
      *
      * IMPORTANT: by default, the original (native) type for this value
      * are NOT included. So it's quite possible to get an empty set here.
+     * Also, type order in the result set MAKES SENSE so keep it stable and do not change without reason
      */
     fun getStableTypes(key: DataFlowValue): Set<KotlinType>
 

compiler/frontend/src/org/jetbrains/kotlin/resolve/calls/smartcasts/DelegatingDataFlowInfo.kt

@@ -122,12 +122,12 @@ internal class DelegatingDataFlowInfo private constructor(
 
         val enrichedTypes = newLinkedHashSetWithExpectedSize<KotlinType>(types.size + 1)
         val originalType = key.type
-        if (originalType.isMarkedNullable) {
-            enrichedTypes.add(TypeUtils.makeNotNullable(originalType))
-        }
         for (type in types) {
             enrichedTypes.add(TypeUtils.makeNotNullable(type))
         }
+        if (originalType.isMarkedNullable) {
+            enrichedTypes.add(TypeUtils.makeNotNullable(originalType))
+        }
 
         return enrichedTypes
     }