FIR. Refactor smart-cast representation in FIR tree

Make smart-casts non-transparent expression without delegation
to underlying FirQualifiedAccessExpression, as children delegation in
fir tree has unclear semantics
Remove two different kinds of tree nodes for smart-casts

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/calls/ResolutionDiagnostic.kt

@@ -9,8 +9,8 @@ import org.jetbrains.kotlin.KtSourceElement
 import org.jetbrains.kotlin.fir.declarations.FirFunction
 import org.jetbrains.kotlin.fir.declarations.FirValueParameter
 import org.jetbrains.kotlin.fir.expressions.FirExpression
-import org.jetbrains.kotlin.fir.expressions.FirExpressionWithSmartcast
 import org.jetbrains.kotlin.fir.expressions.FirNamedArgumentExpression
+import org.jetbrains.kotlin.fir.expressions.FirSmartCastExpression
 import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirNamedFunctionSymbol
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
@@ -103,7 +103,7 @@ object LowerPriorityForDynamic : ResolutionDiagnostic(K2_SYNTHETIC_RESOLVED)
 
 object CandidateChosenUsingOverloadResolutionByLambdaAnnotation : ResolutionDiagnostic(RESOLVED)
 
-class UnstableSmartCast(val argument: FirExpressionWithSmartcast, val targetType: ConeKotlinType, val isCastToNotNull: Boolean) :
+class UnstableSmartCast(val argument: FirSmartCastExpression, val targetType: ConeKotlinType, val isCastToNotNull: Boolean) :
     ResolutionDiagnostic(UNSTABLE_SMARTCAST)
 
 class ArgumentTypeMismatch(

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/VariableStorageImpl.kt

@@ -62,7 +62,7 @@ class VariableStorageImpl(private val session: FirSession) : VariableStorage() {
 
     private fun FirElement.unwrapElement(): FirElement = when (this) {
         is FirWhenSubjectExpression -> whenRef.value.let { it.subjectVariable ?: it.subject }?.unwrapElement() ?: this
-        is FirExpressionWithSmartcast -> originalExpression.unwrapElement()
+        is FirSmartCastExpression -> originalExpression.unwrapElement()
         is FirSafeCallExpression -> selector.unwrapElement()
         is FirCheckedSafeCallSubject -> originalReceiverRef.value.unwrapElement()
         is FirCheckNotNullCall -> argument.unwrapElement()

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/CFGNode.kt

@@ -857,3 +857,12 @@ object FirStub : FirElement {
         return this
     }
 }
+
+
+// ----------------------------------- Smart-cast node -----------------------------------
+
+class SmartCastExpressionExitNode(owner: ControlFlowGraph, override val fir: FirSmartCastExpression, level: Int, id: Int) : CFGNode<FirSmartCastExpression>(owner, level, id) {
+    override fun <R, D> accept(visitor: ControlFlowGraphVisitor<R, D>, data: D): R {
+        return visitor.visitSmartCastExpressionExitNode(this, data)
+    }
+}

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/CFGNodeRenderer.kt

@@ -44,6 +44,7 @@ fun CFGNode<*>.render(): String =
                 is ResolvedQualifierNode -> "Access qualifier ${fir.classId}"
                 is ComparisonExpressionNode -> "Comparison ${fir.operation.operator}"
                 is TypeOperatorCallNode -> "Type operator: \"${CfgRenderer.renderElementAsString(fir)}\""
+                is SmartCastExpressionExitNode -> "Smart cast: \"${CfgRenderer.renderElementAsString(fir)}\""
                 is EqualityOperatorCallNode -> "Equality operator ${fir.operation.operator}"
                 is JumpNode -> "Jump: ${fir.render()}"
                 is StubNode -> "Stub"

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/cfg/ControlFlowGraphVisitor.kt

@@ -386,4 +386,8 @@ abstract class ControlFlowGraphVisitor<out R, in D> {
     open fun visitAnnotationExitNode(node: AnnotationExitNode, data: D): R {
         return visitNode(node, data)
     }
+
+    open fun visitSmartCastExpressionExitNode(node: SmartCastExpressionExitNode, data: D): R {
+        return visitNode(node, data)
+    }
 }

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/dfa/util.kt

@@ -99,6 +99,7 @@ val FirElement.symbol: FirBasedSymbol<*>?
         is FirDeclaration -> symbol
         is FirWhenSubjectExpression -> whenRef.value.subject?.symbol
         is FirSafeCallExpression -> selector.symbol
+        is FirSmartCastExpression -> originalExpression.symbol
         else -> null
     }?.takeIf {
         (this as? FirExpression)?.unwrapSmartcastExpression() is FirThisReceiverExpression ||
@@ -116,6 +117,6 @@ internal val FirResolvable.symbol: FirBasedSymbol<*>?
 
 fun FirExpression.unwrapSmartcastExpression(): FirExpression =
     when (this) {
-        is FirExpressionWithSmartcast -> originalExpression
+        is FirSmartCastExpression -> originalExpression
         else -> this
     }