K2: use ClassKind.CLASS for object literals

K1 uses CLASS, and libraries like kotlinx-metadata-jvm and
kotlin-reflect already rely on it.

 #KT-57641 Fixed

compiler/testData/codegen/box/reflection/classes/objectInstance.kt

@@ -29,6 +29,7 @@ fun box(): String {
     assertEquals(null, C::class.objectInstance)
     assertEquals(null, String::class.objectInstance)
     assertEquals(Unit, Unit::class.objectInstance)
+    assertEquals(null, object {}::class.objectInstance)
 
     return "OK"
 }