[FIR] Fix transform of subject of when expressions with subject variable

compiler/fir/tree/gen/org/jetbrains/kotlin/fir/expressions/impl/FirWhenExpressionImpl.kt

@@ -58,6 +58,7 @@ internal class FirWhenExpressionImpl(
     override fun <D> transformSubject(transformer: FirTransformer<D>, data: D): FirWhenExpressionImpl {
         if (subjectVariable != null) {
             subjectVariable = subjectVariable?.transformSingle(transformer, data)
+            subject = subjectVariable?.initializer
         } else {
             subject = subject?.transformSingle(transformer, data)
         }

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/implementation.kt

@@ -266,6 +266,7 @@ fun SmartPrinter.printImplementation(implementation: Implementation) {
                                 """
                                 |if (subjectVariable != null) {
                                 |            subjectVariable = subjectVariable?.transformSingle(transformer, data)
+                                |            subject = subjectVariable?.initializer
                                 |        } else {
                                 |            subject = subject?.transformSingle(transformer, data)
                                 |        }