FIR DFA: store stability in RealVariable

As part of this change, we also extend the usage of RealVariable in more
places during DFA. Now mutable properties, property with custom getters,
delegated properties, etc are also treatd as a `RealVariable`. In
general this is needed in order to carry out smartcast computation in
order to report `SMARTCAST_IMPOSSIBLE`. It seems to also have side
effects that improves behavior of some test files.

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/FirExpressionWithSmartcastToNull.kt

@@ -29,11 +29,11 @@ abstract class FirExpressionWithSmartcastToNull : FirExpressionWithSmartcast() {
     abstract override val explicitReceiver: FirExpression?
     abstract override val dispatchReceiver: FirExpression
     abstract override val extensionReceiver: FirExpression
-    abstract override val smartcastType: FirTypeRef
-    abstract override val smartcastStability: SmartcastStability
     abstract override val originalExpression: FirQualifiedAccessExpression
     abstract override val typesFromSmartCast: Collection<ConeKotlinType>
     abstract override val originalType: FirTypeRef
+    abstract override val smartcastType: FirTypeRef
+    abstract override val smartcastStability: SmartcastStability
 
     override fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R = visitor.visitExpressionWithSmartcastToNull(this, data)
 

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/NodeConfigurator.kt

@@ -471,6 +471,8 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
             +field("originalExpression", qualifiedAccessExpression)
             +field("typesFromSmartCast", "Collection<ConeKotlinType>", null, customType = coneKotlinTypeType)
             +field("originalType", typeRef)
+            +field("smartcastType", typeRef)
+            +smartcastStability
         }
 
         safeCallExpression.configure {