FIR DFA: fix logic clear aliasing

The logic should clear back aliases as well. To ensure all back aliases
don't lose any information, statements on the original variable are
copied over to its aliases.

idea/idea-frontend-fir/idea-fir-low-level-api/tests/org/jetbrains/kotlin/idea/fir/low/level/api/diagnostic/compiler/based/DiagnosisCompilerTestFE10TestdataTestGenerated.java

@@ -28217,6 +28217,12 @@ public class DiagnosisCompilerTestFE10TestdataTestGenerated extends AbstractDiag
                     runTest("compiler/testData/diagnostics/tests/smartCasts/variables/accessorAndFunction.kt");
                 }
 
+                @Test
+                @TestMetadata("aliasing.kt")
+                public void testAliasing() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/smartCasts/variables/aliasing.kt");
+                }
+
                 @Test
                 public void testAllFilesPresentInVariables() throws Exception {
                     KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/diagnostics/tests/smartCasts/variables"), Pattern.compile("^(.+)\\.kt$"), Pattern.compile("^(.+)\\.fir\\.kts?$"), true);

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/components/KtFirSmartcastProvider.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.fir.expressions.FirExpressionWithSmartcast
 import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
 import org.jetbrains.kotlin.fir.types.ConeKotlinType
 import org.jetbrains.kotlin.fir.types.coneTypeSafe
+import org.jetbrains.kotlin.fir.types.isStableSmartcast
 import org.jetbrains.kotlin.idea.fir.low.level.api.api.getOrBuildFirSafe
 import org.jetbrains.kotlin.idea.frontend.api.ImplicitReceiverSmartCast
 import org.jetbrains.kotlin.idea.frontend.api.ImplicitReceiverSmartcastKind
@@ -41,13 +42,13 @@ internal class KtFirSmartcastProvider(
             (extensionReceiver !is FirExpressionWithSmartcast || !extensionReceiver.isStable)
         ) return emptyList()
         buildList {
-            (dispatchReceiver as? FirExpressionWithSmartcast)?.takeIf { it.isStable }?.let { smartCasted ->
+            dispatchReceiver.takeIf { it.isStableSmartcast() }?.let { smartCasted ->
                 ImplicitReceiverSmartCast(
                     smartCasted.typeRef.coneTypeSafe<ConeKotlinType>()?.asKtType() ?: return@let null,
                     ImplicitReceiverSmartcastKind.DISPATCH
                 )
             }?.let(::add)
-            (extensionReceiver as? FirExpressionWithSmartcast)?.takeIf { it.isStable }?.let { smartCasted ->
+            extensionReceiver.takeIf { it.isStableSmartcast() }?.let { smartCasted ->
                 ImplicitReceiverSmartCast(
                     smartCasted.typeRef.coneTypeSafe<ConeKotlinType>()?.asKtType() ?: return@let null,
                     ImplicitReceiverSmartcastKind.EXTENSION