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

compiler/testData/diagnostics/tests/smartCasts/varnotnull/unnecessary.fir.kt

@@ -1,12 +0,0 @@
-fun String?.foo(): String {
-    return this ?: ""
-}
-
-class MyClass {
-    private var s: String? = null
-
-    fun bar(): String {
-        s = "42"
-        return s.foo()
-    }    
-}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/unnecessary.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 fun String?.foo(): String {
     return this ?: ""
 }

compiler/testData/diagnostics/tests/smartCasts/varnotnull/unnecessaryWithBranch.fir.kt

@@ -1,12 +0,0 @@
-fun String?.foo(): String {
-    return this ?: ""
-}
-
-class MyClass {
-    fun bar(): String {
-        var s: String? = null
-        if (4 < 2)
-            s = "42"
-        return s.foo()
-    }    
-}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/unnecessaryWithBranch.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 fun String?.foo(): String {
     return this ?: ""
 }