iOS port, quantity keypad does not have buttons for decimal or minus

As I am working on the iOS port, I notice that the keypad for entering quantities does not have a period, comma, or dash, to enter quantities like `0.01` or `-1`.

There are issues with adding either of the decimal or negation.

Adding decimal option still presents a nice numpad, but I don't think it will offer users both of period and comma. Potentially I would hard-code the app to provide period, and maybe add extra buttons in an AppBar menu, such as the comma, when applicable.

Adding an option for negation seems to force iOS to present a full keyboard, which seems less useful for adding quantities quickly. Again I could add a button in an AppBar menu to enter the negation sign `-`.

Perhaps there should be an option in menu to toggle the keyboard altogether. Effectively a toggle on the negation option.

Start by locating the iOS quantity-entry keypad and reproduce the missing period, comma, and minus controls on iOS. Review how the current keypad handles decimal and negation input; done means users can enter decimal and negative quantities while retaining a quick numeric keypad experience.

Written by the indexing model from the issue text.