Focus to previous node on backspace on empty field.

[ainulbedjo]

Opened a PR from this issue : #12.

So basically, you can't listen to backspace on empty textfield (source) even with this code below it doesnt work (on my machine tho).

// Listens for backspace key event when textfield is empty. Moves to previous node if possible.
    return RawKeyboardListener(
        focusNode: FocusNode(),
        onKey: (value) {
          if (value.logicalKey.keyLabel == 'Backspace') {
            changeFocusToPreviousNodeWhenTapBackspace();
          }
        },
        child: generateTextFields(context));

I make this workaround by making the textField limit to 2 and set an empty character \u200b to it. So when user pressed the backspace, it listen to it, and direct the focus to previous textfield.

[ainulbedjo]

Hi @david-legend,
could you review this PR? thanks

[david-legend]

checking soon