Observable group extensions

[vgromfeld]

It follows #3201 and add some extensions methods to simplify the operations on ObservableGroupedCollection<TKey, TValue>.

PR Type

What kind of change does this PR introduce?

• Feature

What is the new behavior?

This PR adds a set of extensions methods to simplify the add/insert/replace/remove operations on ObservableGroupedCollection<TKey, TValue>.

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)
• If new feature, add to Feature List
• Contains NO breaking changes

[ghost]

Thanks vgromfeld 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]

Awesome! 🎉

I also think I have some optimizations to throw on top of most of these extensions by leveraging the fact that the ObservableCollection<T> type is almost always using a List<T> internally, which implements a struct enumerator - we can use that to achieve a faster and allocation free implementation of these new LINQ-style extensions 🚀

Looking forward to this getting merged, then I'll create another PR with those new tweaks!