Fix ambiguous queue_material_tilemap_meshes ordering

[MeoMix]

It was possible for queue_material_tilemap_meshes to run prior to prepare which would result in nothing rendering.

This would only occur in scenarios where other code inserted a system dependent on mut commands: Commands into the Queue set. The bevy-egui library was doing so and was thus introducing behavior where bevy-ecs-tilemap would intermittently not render anything due to improper system ordering.

Fixes: #521

Additional Details

djeedai/bevy_hanabi#297 Bevy Hanabi experienced a similar issue. Their fix looks similar to this proposed fix.

The Bevy notes hint that this sort of change is necessary, too:

This is not directly an issue with automatically applying command buffers. It is related, but the key issue here is one of improper system ordering. The existing codebase happened to work but was not guaranteed to work. It worked only because the scheduler was choosing to resolve ambiguous system ordering in a way which was compatible with bevy_ecs_tilemap architecture. This invited the problem where third party code could introduce systems that would affect the scheduler's ordering decision and result in rendering failures.

[StarArawn]

@MeoMix can you run cargo fmt on this and then it's good to merge!

[MeoMix]

@StarArawn Feel free to merge? I don't have the permission to do so