Updated the NumberBox ValueProperty's default BindingMode to be TwoWay

[syntax-tm]

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

Currently, a Binding to the NumberBox.Value is OneWay by default. The Source (DataContext) raising an INotifyPropertyChanged event will trigger a change in the NumberBox. However, a change in the NumberBox will not update the Source.

If you are binding to the NumberBox.Value (using the default BindingMode, OneWay):

• The increment, decrement, and clear operations are not updating the Source
  • This is made worse by the fact the Text displayed will not match the actual Value
  • The Value property of the NumberBox changing means that will no longer match the Source property
• Manually inputting (typing) a number does not update the Source property

I created a test project to demonstrate this, but here's some screenshots that show the issue that currently exists (OneWay) and then the solution (TwoWay).

WpfDemoApp.zip

What is the new behavior?

• NumberBox.Value default BindingMode is now TwoWay and functions as expected

Other information

I was surprised that this wasn't already set for this control and I'm not sure if there's any reasoning for why that is but here's an excerpt from the MSDN docs on BindingMode regarding the default bindings of "user-editable control properties":

The default is Default, which returns the default binding mode value of the target dependency property. However, the default value varies for each dependency property. In general, user-editable control properties, such as those of text boxes and check boxes, default to two-way bindings, whereas most other properties default to one-way bindings. (source)

[cla-bot]

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have the users @syntax-tm on file. In order for us to review and merge your code, please contact the project maintainers to get yourself added.

[syntax-tm]

I'm not sure what method of contact you guys prefer for the signing the Contributor License Agreement, but if it's possible you can consider this my acceptance of the agreement. If there's anything more you need from me just let me know. Thanks!

[syntax-tm]

Do you want me to revert the last merge and rebase off of the latest?