[FIR] Completely unwrap original argument when computing type arguments

When computing the conversion type for a type operator call, the
argument needs to be fully unwrapped before getting the resolved type.
This avoids the situation when the argument is a when-subject and the
assumed original type is not correct. Before, only smart-casts were
unwrapped, and this change will also unwrap when-subjects (as well as a
few other FirExpressions).

^KT-62114 Fixed

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt

@@ -839,7 +839,7 @@ open class FirExpressionsResolveTransformer(transformer: FirAbstractBodyResolveT
         val firClass = type.lookupTag.toSymbol(session)?.fir ?: return this
         if (firClass.typeParameters.isEmpty()) return this
 
-        val originalType = argument.unwrapSmartcastExpression().resolvedType
+        val originalType = argument.unwrapExpression().resolvedType
         val newType = components.computeRepresentativeTypeForBareType(type, originalType)
             ?: if (firClass.isLocal && (operation == FirOperation.AS || operation == FirOperation.SAFE_AS)) {
                 (firClass as FirClass).defaultType()