Kernel: Let InodeWatcher track child inode numbers instead of names

First of all, this fixes a dumb info leak where we'd write kernel heap
addresses (StringImpl*) into userspace memory when reading a watcher.

Instead of trying to pass names to userspace, we now simply pass the
child inode index. Nothing in userspace makes use of this yet anyway,
so it's not like we're breaking anything. We'll see how this evolves.

Kernel/FileSystem/Ext2FileSystem.cpp

@@ -1027,7 +1027,7 @@ KResult Ext2FSInode::add_child(Inode& child, const StringView& name, mode_t mode
     if (success)
         m_lookup_cache.set(name, child.index());
 
-    did_add_child(name);
+    did_add_child(child.identifier());
     return KSuccess;
 }
 
@@ -1072,7 +1072,7 @@ KResult Ext2FSInode::remove_child(const StringView& name)
     if (result.is_error())
         return result;
 
-    did_remove_child(name);
+    did_remove_child(child_id);
     return KSuccess;
 }