Introduce FIR_IDENTICAL for FIR vs old frontend tests #KT-36879 Fixed

compiler/testData/diagnostics/testsWithStdLib/smartcasts/listOfGeneric.fir.kt

@@ -1,8 +0,0 @@
-// See KT-9529 Smart cast causes code to be incompilable
-
-fun <T : Any> foo(o: T): Collection<T> {
-    if (o is String) {
-        return listOf(o)
-    }
-    return listOf(o)
-}

compiler/testData/diagnostics/testsWithStdLib/smartcasts/listOfGeneric.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // See KT-9529 Smart cast causes code to be incompilable
 
 fun <T : Any> foo(o: T): Collection<T> {