Fix RadialGauge default template value formatting

[jeromelaban]

PR Type

What kind of change does this PR introduce?
Bugfix

What is the current behavior?

Changing the RadialGauge.ValueStringFormat does not have an effect on the displayed value.

What is the new behavior?

This update fixes the RadialGauge value text formatting that was overridden by a template binding on the Value property.

Here's the appropriate text update location:

https://github.com/windows-toolkit/WindowsCommunityToolkit/blob/ef6527227539362125a0617d9b9821b2c009e11e/Microsoft.Toolkit.Uwp.UI.Controls/RadialGauge/RadialGauge.cs#L537

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Pull Request has been submitted to the documentation repository instructions. Link:
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

Other information

[ghost]

Thanks jeromelaban for opening a Pull Request! The reviewers will test the PR and highlight if there is any conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌

[vgromfeld]

You should also update the code behind to force a refresh of valueText.Text when ValueStringFormatProperty value changes.

In the actual implementation, the formatting is refreshed only when radialGauge.Value is changed (through override void OnValueChanged(double oldValue, double newValue)).

[michael-hawker]

@jeromelaban did you want to make the fix suggested by @vgromfeld as well?

[jeromelaban]

@michael-hawker yes, just got some time to finish it and update the sample to test it as well :)

[michael-hawker]

Thanks for catching and fixing this @jeromelaban! 🦙❤