FIR checker: apply override checker to anonymous objects

^KT-44695 Fixed

compiler/testData/diagnostics/tests/enum/openMemberInEnum.fir.kt

@@ -1,17 +0,0 @@
-enum class EnumWithOpenMembers {
-    E1 {
-        override fun foo() = 1
-        override val bar: String = "a"
-    },
-
-    E2 {
-        override fun f() = 3
-        override val b = 4
-    };
-
-    open fun foo() = 1
-    open val bar: String = ""
-
-    fun f() = 2
-    val b = 3
-}

compiler/testData/diagnostics/tests/enum/openMemberInEnum.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 enum class EnumWithOpenMembers {
     E1 {
         override fun foo() = 1