FIR2IR: standardize expression with smart cast conversion

To convert smart cast expression, now we just convert
original expression in standard way and wrap it with TYPE_OP.
Before this commit original expression was converted in different way,
that led to errors e.g. for this expression casting.

compiler/testData/codegen/box/smartCasts/implicitReceiverInWhen.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 
 open class A {
     fun f(): String =