FIR: Change the Fir2Ir handling of smart casts.

Generate the expression with the original type and then insert
an implicit conversion. That matches the behavior of psi2ir
better and therefore avoids breaking backend assumptions.

In particular, IrGetValue expects the type of the underlying
symbol and the type of the IrGetValue to be the same.

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrVisitor.kt

@@ -899,7 +899,18 @@ class Fir2IrVisitor(
     }
 
     override fun visitExpressionWithSmartcast(expressionWithSmartcast: FirExpressionWithSmartcast, data: Any?): IrElement {
-        return visitQualifiedAccessExpression(expressionWithSmartcast, data)
+        // Generate the expression with the original type and then cast it to the smart cast type.
+        val value = expressionWithSmartcast.toIrExpression(expressionWithSmartcast.originalType).applyReceivers(expressionWithSmartcast)
+        val castType = expressionWithSmartcast.typeRef.toIrType(session, declarationStorage)
+        if (value.type == castType) return value
+        return IrTypeOperatorCallImpl(
+            value.startOffset,
+            value.endOffset,
+            castType,
+            IrTypeOperator.IMPLICIT_CAST,
+            castType,
+            value
+        )
     }
 
     override fun visitCallableReferenceAccess(callableReferenceAccess: FirCallableReferenceAccess, data: Any?): IrElement {