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/analysis-api-impl-base/tests/org/jetbrains/kotlin/analysis/api/impl/base/test/cases/components/smartCastProvider/AbstractHLSmartCastInfoTest.kt

@@ -24,6 +24,12 @@ abstract class AbstractHLSmartCastInfoTest : AbstractAnalysisApiSingleFileTest()
                     appendLine("expression: ${expression.text}")
                     appendLine("isStable: ${smartCastInfo?.isStable}")
                     appendLine("smartCastType: ${smartCastInfo?.smartCastType?.render()}")
+
+                    val receiverSmartCasts = expression.getImplicitReceiverSmartCast()
+                    for (receiverSmartCast in receiverSmartCasts) {
+                        appendLine("receiver: ${receiverSmartCast.kind}")
+                        appendLine("    smartCastType: ${receiverSmartCast.type.render()}")
+                    }
                 }
             }
         }