FIR: Unify all references to FIR nodes from non-parents

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/dfa/VariableStorage.kt

@@ -43,10 +43,10 @@ class VariableStorage(private val session: FirSession) {
     }
 
     private fun FirElement.unwrapElement(): FirElement = when (this) {
-        is FirWhenSubjectExpression -> whenSubject.whenExpression.let { it.subjectVariable ?: it.subject }?.unwrapElement() ?: this
+        is FirWhenSubjectExpression -> whenRef.value.let { it.subjectVariable ?: it.subject }?.unwrapElement() ?: this
         is FirExpressionWithSmartcast -> originalExpression.unwrapElement()
         is FirSafeCallExpression -> regularQualifiedAccess.unwrapElement()
-        is FirCheckedSafeCallSubject -> originalReceiverReference.value.unwrapElement()
+        is FirCheckedSafeCallSubject -> originalReceiverRef.value.unwrapElement()
         else -> this
     }
 
@@ -71,7 +71,7 @@ class VariableStorage(private val session: FirSession) {
         val isThisReference: Boolean
         val expression: FirQualifiedAccess? = when (originalFir) {
             is FirQualifiedAccessExpression -> originalFir
-            is FirWhenSubjectExpression -> originalFir.whenSubject.whenExpression.subject as? FirQualifiedAccessExpression
+            is FirWhenSubjectExpression -> originalFir.whenRef.value.subject as? FirQualifiedAccessExpression
             is FirVariableAssignment -> originalFir
             else -> null
         }

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

@@ -122,7 +122,7 @@ internal val FirElement.symbol: AbstractFirBasedSymbol<*>?
     get() = when (this) {
         is FirResolvable -> symbol
         is FirSymbolOwner<*> -> symbol
-        is FirWhenSubjectExpression -> whenSubject.whenExpression.subject?.symbol
+        is FirWhenSubjectExpression -> whenRef.value.subject?.symbol
         is FirSafeCallExpression -> regularQualifiedAccess.symbol
         else -> null
     }?.takeIf { this is FirThisReceiverExpression || (it !is FirFunctionSymbol<*> && it !is FirAccessorSymbol) }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/IntegerLiteralTypeApproximationTransformer.kt

@@ -136,7 +136,7 @@ class IntegerLiteralTypeApproximationTransformer(
         data: ConeKotlinType?
     ): CompositeTransformResult<FirStatement> {
         val newReceiver =
-            checkedSafeCallSubject.originalReceiverReference.value.transform<FirExpression, ConeKotlinType?>(this, data).single
+            checkedSafeCallSubject.originalReceiverRef.value.transform<FirExpression, ConeKotlinType?>(this, data).single
         checkedSafeCallSubject.propagateTypeFromOriginalReceiver(newReceiver, session)
         return super.transformCheckedSafeCallSubject(checkedSafeCallSubject, data)
     }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirControlFlowStatementsResolveTransformer.kt

@@ -125,7 +125,7 @@ class FirControlFlowStatementsResolveTransformer(transformer: FirBodyResolveTran
         whenSubjectExpression: FirWhenSubjectExpression,
         data: ResolutionMode
     ): CompositeTransformResult<FirStatement> {
-        val parentWhen = whenSubjectExpression.whenSubject.whenExpression
+        val parentWhen = whenSubjectExpression.whenRef.value
         val subjectType = parentWhen.subject?.resultType ?: parentWhen.subjectVariable?.returnTypeRef
         if (subjectType != null) {
             whenSubjectExpression.resultType = subjectType

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt

@@ -177,7 +177,7 @@ class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransformer) :
         dataFlowAnalyzer.enterSafeCallAfterNullCheck(safeCallExpression)
 
         safeCallExpression.apply {
-            checkedSubject.value.propagateTypeFromOriginalReceiver(receiver, components.session)
+            checkedSubjectRef.value.propagateTypeFromOriginalReceiver(receiver, components.session)
             transformRegularQualifiedAccess(this@FirExpressionsResolveTransformer, data)
             propagateTypeFromQualifiedAccessAfterNullCheck(receiver, session)
         }