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

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/file/structure/FirElementsRecorder.kt

@@ -9,10 +9,7 @@ import org.jetbrains.kotlin.*
 import org.jetbrains.kotlin.analysis.low.level.api.fir.element.builder.DuplicatedFirSourceElementsException
 import org.jetbrains.kotlin.analysis.low.level.api.fir.util.isErrorElement
 import org.jetbrains.kotlin.fir.FirElement
-import org.jetbrains.kotlin.fir.expressions.FirConstExpression
-import org.jetbrains.kotlin.fir.expressions.FirFunctionCall
-import org.jetbrains.kotlin.fir.expressions.FirPropertyAccessExpression
-import org.jetbrains.kotlin.fir.expressions.FirVariableAssignment
+import org.jetbrains.kotlin.fir.expressions.*
 import org.jetbrains.kotlin.fir.expressions.builder.buildConstExpression
 import org.jetbrains.kotlin.fir.references.*
 import org.jetbrains.kotlin.fir.types.FirErrorTypeRef
@@ -115,6 +112,7 @@ internal open class FirElementsRecorder : FirVisitor<Unit, MutableMap<KtElement,
                         it.kind == KtFakeSourceElementKind.ImplicitConstructor ||
                         it.kind == KtFakeSourceElementKind.DesugaredPrefixNameReference ||
                         it.kind == KtFakeSourceElementKind.DesugaredPostfixNameReference ||
+                        it.kind == KtFakeSourceElementKind.SmartCastExpression ||
                         it.isSourceForCompoundAccess(element)
             }.psi as? KtElement
             ?: return

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosisCompilerFirTestdataTestGenerated.java

@@ -4111,6 +4111,12 @@ public class DiagnosisCompilerFirTestdataTestGenerated extends AbstractDiagnosis
                 public void testSafeCalls() throws Exception {
                     runTest("compiler/fir/analysis-tests/testData/resolve/smartcasts/safeCalls/safeCalls.kt");
                 }
+
+                @Test
+                @TestMetadata("unstableSmartCastOnSafeCallArgument.kt")
+                public void testUnstableSmartCastOnSafeCallArgument() throws Exception {
+                    runTest("compiler/fir/analysis-tests/testData/resolve/smartcasts/safeCalls/unstableSmartCastOnSafeCallArgument.kt");
+                }
             }
 
             @Nested