Add double click on function_pointer

[surreal6]

The idea is to add double click actions (i.e.: to allow navigation in a FileDialog, that requieres double click to enter in a folder)

I added two different ways to solve:

• one to detect double click in the trigger with an exposed debounce time

• another by declaring a button to the complete double click action (safer for reduced mobility, as double clicking in the air is a bit dificult for some people) This second option is ignored if the value is left empty.

Let me know what you think :)

[Malcolmnixon]

The implementation looks reasonable. I wonder whether we should add something similar to poke.gd so people can trigger a double-tap with their finger. The duration would probably need to be a little longer due to no physical surface to use; although with the new haptic-system coming in it'll be easier to "feel" the touch and repeat a second one.

[BastiaanOlij]

@Malcolmnixon to revisit this, looks good in general, we do feel the timer solution needs to change because there are situations this will fall over.