Add unary operator

[arcadiogarcia]

Fixes

Fixes #3523

Introduce UnaryOperator to animation expressions, a new type of operation that only expects one operator, to fix the issue where the ! operator failed because it expected 2 operators like the other (non-unary) operators.

PR Type

What kind of change does this PR introduce?

Bugfix

What is the current behavior?

With the current version of the toolkit, code like

    var visual = Windows.UI.Xaml.Hosting.ElementCompositionPreview.GetElementVisual(this);
    var a = !(visual.GetReference().Offset.X > 10);
    visual.StartAnimation("Offset.Y", ExpressionFunctions.Conditional(a, 1,2));

will throw this exception
Can't have an operator that doesn't have 2 exactly params

What is the new behavior?

After these changes, no exception is thrown and the correct animation expression is generated

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 arcadiogarcia 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 🙌

[Sergio0694]

Looks great! 🚀

[ghost]

Hello @Sergio0694!

Because this pull request has the auto merge label, I will be glad to assist with helping to merge this pull request once all check-in policies pass.

p.s. you can customize the way I help with merging this pull request, such as holding this pull request until a specific person approves. Simply @mention me (@msftbot) and give me an instruction to get started! Learn more here.