🐛 NumberBox format function breaks it if num.tryParse can not parse the text

[HarsimranVirk]

Describe the bug
NumberBox format function fails if we add commas or $ in the formatted text. Something like $200,000 will break the widget and it will not change state anymore.

To Reproduce
Steps to reproduce the behavior:
Use NumberFormat.currency().format as the format function, NumberBox will be broken.

Expected behavior
If users are given the option to have any arbitrary format function, then the assumption that num.tryParse() will be able to parse the formatted text back to a num value is incorrect.

[HarsimranVirk]

We can add an additional reverseFormat function to let users define how to parse their formatted text back to a num value

[bdlukaa]

This behavior is not encountered in the Native implementation.