Some ideas for small usability improvements

[FlooferLand]

Hello, its me again! (managed to get the latest actionlike version working via git)
Here are some things I'd really appreciate that wouldn't be too trivial to implement:

1. Adding optional tuple support to InputMap.insert
   • Bevy does "functions that can take in a singular value or a tuple" a lot
   • It would let you do things like this (I originally tried this but it didn't work)

     input_map.insert(GamePlayerAction::Crouch, (KeyCode::ControlLeft, KeyCode::ControlRight));

   • insert_dual_axis could benefit from this, it would be cleaner/simpler if you were able to do the following to add in a virtual mapping:

     input_map.insert_dual_axis(GamePlayerAction::Move, (KeyCode::A, KeyCode::D));

2. MouseVirtualAxis (and OtherVirtualAxis?)
   • In some cases people might want to map the mouse buttons to an axis (I originally tried this while setting up zooming using the mouse wheel, though MouseScrollAxis does exist).
   • PS: I think combining the (Mouse/Keyboard/Gamepad)VirtualAxis type into a general VirtualAxis type would be neater. Same with the *Dpad/*Dpad3d types
3. Perhaps more features/examples for player-bindable controls?

[alice-i-cecile]

1. Would be nice, but will hurt compile times more than is really worth it. Once Rust has real variadics support I would love to add this.
2. I'm on board with this; please submit a PR or dedicated issue.
3. Totally agree: this is the last key workflow that we really need to polish and teach.

[FlooferLand]

Made one at #632!
Originally tried making a PR but I couldn't get my head around why it was telling me that Bevy's KeyCode doesn't implement Buttonlike (even though it does!)