inpututil: add a function to get the last touch position just before releasing

[hajimehoshi]

Requested by @midorimici

[divVerent]

Yes! I am currently emulating this myself with some hacky code.

[hajimehoshi]

If someone wants to work on this, please discuss what API we want before starting to implement it.

[hajimehoshi]

I'm still not sure what API would be the best. What about

func AppendJustReleasedTouchIDs(touchIDs []ebiten.TouchID) []ebiten.TouchID
func TouchPositionInPreviousTick(id ebiten.TouchID) (int, int, bool)

?

[hajimehoshi]

Treating touches as IDs itself seems a not good idea in the first place 🤔