K2: add package FQ name to ClassId of anonymous objects

This is needed because in order to figure out which declarations are
visible from anonymous objects in terms of overridability (see
`FirVisibilityChecker.isVisibleForOverriding`), we need to get the
package name of that anonymous object, because there's package-private
visibility on JVM.

 #KT-62017 Fixed

compiler/testData/codegen/box/package/kt62017.kt

@@ -0,0 +1,20 @@
+// TARGET_BACKEND: JVM
+// FILE: a/A.java
+
+package a;
+
+abstract class A<T> {
+    String o() { return "O"; }
+    String k() { return "K"; }
+}
+
+// FILE: a/1.kt
+
+package a
+
+private val o = object : A<String>() {}
+
+fun box(): String {
+    val k = object : A<String>() {}
+    return o.o() + k.k()
+}