Refactor systems with using SystemData

[vladbat00]

There are some systems that are good candidates for introducing a separate SystemData struct for them: such systems require a lot of resources and pass them around their helper functions (making those functions' argument list really huge).

Some examples of bad systems:
bins/client/src/ecs/systems/input.rs
bins/client/src/ecs/systems/client_network.rs

Some examples of good systems:
libs/game/src/ecs/systems/monster/spawner.rs

Note that you shouldn't refactor all the systems in one pull request. As it's a "good first issue", just look through the systems and pick the one which you think will be feasible for you to tackle. But nothing stops you to make more than one PR, of course. :)