Use in modifier for .Set() and .SetAutoOverride()

[BeanCheeseBurrito]

All .Set() and .SetAutoOverride() overloads have been changed to use the in parameter modifier to pass in component data.

Below are all valid ways of setting components.

Position position = new Position(1, 2);

Entity entity = world.Entity();
entity.Set(position);     // Pass by value.
entity.Set(in position);  // Pass by in reference.
entity.Set(ref position); // Pass by ref reference but a warning is issued.