Handle cases of state interfaces with different data types

[saikishor]

Needs ros-controls/ros2_control#2351

[christophfroehlich]

LGTM, should we also add a test for that?

[destogl]

I was thinking to approach this in another way. I think we should have per default conversion between double and other types (if possible). This will help us with the reusability of HW interface and controllers. We had similar issues in CAN implementation and solved it with memcpy — there we have uint32_t variables for “transport storage”. I know this is not beautiful, but it is extremely useful. We should give a warning once per interface that we are handing the type using double but it is a compatible type and then just do it. Otherwise, I am afraid that we will end up in the endless if - else if loops and having many issues with the controllers — HW incompatibilities, even though they could work with the proposed type support.

What I want to say, we should add this casting to the handles and not in the controllers.