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

compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/privateClassFunctionOverriddenByProperty.fir.kt

@@ -1,8 +0,0 @@
-open class B {
-    private fun getX() = 1
-}
-
-class C : B() {
-    val x: Int
-        get() = 1
-}

compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/privateClassFunctionOverriddenByProperty.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 open class B {
     private fun getX() = 1
 }