[FIR]: Set proper classId to enum entries

FirVisibilityChecker::isVisible checked if a private declaration can be
accessed at a use site by matching class ids of the private
declaration's owner with the use site's containing class
declarations. When the private declaration is defined in an enum
entry and used in the same entry, its owner class id has the enum
entry name, but the use site is in an FirAnonymousObject, which has
"anonymous" as the class id. This causes visibility check to fail.

This PR fixes owner class ids of declarations defined in enum entries
to be the same as normal anonymous objects.

compiler/testData/codegen/box/enum/enumEntryMembers.kt

@@ -3,6 +3,10 @@
 // FILE: lib.kt
 enum class Foo {
     FOO() {
+        // Test for KT-42351
+        private fun privateBar() = "bar"
+        override fun bar(): String = privateBar()
+
         override fun foo() = "foo"
        
         override var xxx: String
@@ -12,6 +16,7 @@ enum class Foo {
     };
 
     abstract fun foo(): String
+    abstract fun bar(): String
     abstract var xxx: String
 }
 
@@ -25,6 +30,7 @@ fun box(): String {
     assertEquals(Foo.FOO.xxx, "xxx")
     assertEquals(Foo.FOO.toString(), "FOO")
     assertEquals(Foo.valueOf("FOO").toString(), "FOO")
+    assertEquals(Foo.FOO.bar(), "bar")
     return "OK"
 }