fix missing header unordered_map

[youmanyousef]

In the level_scene cpp module, there is a missing header file <unordered_map>, and an undeclared reference to it.

editor/level_scene.cppm:1087:10: error: missing '#include <unordered_map>'; 'unordered_map' must be declared before it is used
 1087 |     std::unordered_map<uint64_t, material> m_material_icons;
      |          ^

Adding the header file for it resolves the issue.

[SpinnerX]

Looks good. Merging this change.