[IR] Align captured receiver variable naming with old BE

compiler/testData/ir/irText/classes/lambdaInDataClassDefaultParameter.txt

@@ -6,7 +6,7 @@ FILE fqName:<root> fileName:/lambdaInDataClassDefaultParameter.kt
         EXPRESSION_BODY
           FUN_EXPR type=@[ExtensionFunctionType] kotlin.Function2<<root>.A, kotlin.String, kotlin.Unit> origin=LAMBDA
             FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> ($receiver:<root>.A, it:kotlin.String) returnType:kotlin.Unit
-              $receiver: VALUE_PARAMETER name:<this> type:<root>.A
+              $receiver: VALUE_PARAMETER name:$this$null type:<root>.A
               VALUE_PARAMETER name:it index:0 type:kotlin.String
               BLOCK_BODY
                 RETURN type=kotlin.Nothing from='local final fun <anonymous> (it: kotlin.String): kotlin.Unit declared in <root>.A.<init>'