LibGUI: Preserve correct child order in FileSystemModel

When handling child creation in FileSystemModel, the new child should
be inserted such that the children still follow the correct order of
being grouped by directory-and-file and then sorted alphabetically,
instead of just being appended at the end.

Userland/Libraries/LibGUI/FileSystemModel.cpp

@@ -415,18 +415,33 @@ void FileSystemModel::handle_file_event(Core::FileWatcherEvent const& event)
             break;
         }
 
-        int child_count = parent->m_children.size();
-
         auto& mutable_parent = const_cast<Node&>(*parent);
         auto maybe_child = mutable_parent.create_child(child_name);
         if (!maybe_child)
             break;
 
-        begin_insert_rows(parent->index(0), child_count, child_count);
-
         auto child = maybe_child.release_nonnull();
+
+        bool const is_new_child_dir = S_ISDIR(child->mode);
+        int insert_index = 0;
+        for (auto const& other_child : mutable_parent.m_children) {
+            bool const is_other_child_dir = S_ISDIR(other_child->mode);
+            if (!is_new_child_dir && is_other_child_dir) {
+                ++insert_index;
+                continue;
+            }
+            if (is_new_child_dir && !is_other_child_dir)
+                break;
+
+            if (other_child->name.view() > child_name)
+                break;
+            ++insert_index;
+        }
+
+        begin_insert_rows(parent->index(0), insert_index, insert_index);
+
         mutable_parent.total_size += child->size;
-        mutable_parent.m_children.append(move(child));
+        mutable_parent.m_children.insert(insert_index, move(child));
 
         end_insert_rows();
         break;