Add NumberBox Widget

[WinXaito]

Pre-launch Checklist

• I have updated CHANGELOG.md with my changes
• I have run "dart format ." on the project
• I have added/updated relevant documentation

Need to do:

• Update value with mouse scroll
• Update value with PageUp / PageDown shortcut
• Add documentation
• Add disabled options
• Theme ??

Demo:

[bdlukaa]

This looks awesome, but a few things are missing.

Text formatting. Just exposing TextBox.inputFormatters and adding an example should do the job.

TextBox.keyboardType should be number.

Exposing some other TextBox properties, such as placeholder, autoFocus, cursor-related properties, and other that may be relevant.

[WinXaito]

Text formatting. Just exposing TextBox.inputFormatters and adding an example should do the job.

Currently, the value must be an int, I will try to make a Generic combobox that accept num (So int or double). I have tested that but I'm not satisfied.

Maybe I'll leave it like that for now and do another PR to make this Widget generic. @bdlukaa What do you think about that ?

And I will also do another PR (Because I think that it is necessary to keep it at a reasonable size) for add some property like min/max.

[bdlukaa]

Sounds ok to me!