[FIR] Fix exhaustiveness checking for conditions with equals to object

#KT-37488 Fixed

compiler/testData/diagnostics/tests/sealed/ExhaustiveWhenOnNestedSealed.fir.kt

@@ -1,20 +0,0 @@
-sealed class Sealed {
-    object First: Sealed()
-    sealed class NonFirst {
-        object Second: NonFirst()
-        object Third: NonFirst()
-        object Fourth: Sealed()
-    }    
-}
-
-fun foo(s: Sealed, nf: Sealed.NonFirst): Int {
-    val si = when(s) {
-        Sealed.First -> 1
-        Sealed.NonFirst.Fourth -> 4
-    }
-    val nfi = when(nf) {
-        Sealed.NonFirst.Second -> 2
-        Sealed.NonFirst.Third -> 3
-    }
-    return si <!UNRESOLVED_REFERENCE!>+<!> nfi
-}

compiler/testData/diagnostics/tests/sealed/ExhaustiveWhenOnNestedSealed.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 sealed class Sealed {
     object First: Sealed()
     sealed class NonFirst {