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

compiler/testData/diagnostics/testsWithStdLib/contracts/fromStdlib/synchronize.fir.kt

@@ -1,11 +0,0 @@
-// !LANGUAGE: +ReadDeserializedContracts +UseCallsInPlaceEffect
-
-fun test(lock: Any) {
-    val x: Int
-
-    synchronized(lock) {
-        x = 42
-    }
-
-    x.inc()
-}

compiler/testData/diagnostics/testsWithStdLib/contracts/fromStdlib/synchronize.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !LANGUAGE: +ReadDeserializedContracts +UseCallsInPlaceEffect
 
 fun test(lock: Any) {