WinUI - Fix DataGrid scroll performance issue

[adamplonka]

Fixes #2122

Fixes DataGrid scroll performance issue for large data sources.

PR Type

What kind of change does this PR introduce?

Bugfix

What is the current behavior?

The DataSource set in DataGridDataConnection class is (almost) always of type ICollectionView which implements generic IList<> but doesn't implement IList. This causes fallback to list enumeration to reach the current index..

https://user-images.githubusercontent.com/35062625/231341802-cf6072c8-2ed7-4426-86ea-ac3d8733cb4b.mp4

What is the new behavior?

The fix adds support for ICollectionView DataSource and accesses the items directly by their index. An approach for PagedCollectionView (from Silverlight) can be merged with the fix as it implements the same interface.

https://user-images.githubusercontent.com/35062625/231342564-3ea0703c-980a-4a62-be40-bfdc32570266.mp4

PR Checklist

Please check if your PR fulfills the following requirements:

• [x] Created a feature/dev branch in your fork (vs. submitting directly from a commit on main)
• [x] Based off latest main branch of toolkit
• [x] Tested code with current supported SDKs
• [x] Contains NO breaking changes

Other information

[ghost]

Thanks PlonkaAdam 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 🙌

[adamplonka]

@dotnet-policy-service agree

[Trolldemorted]

This PR has been open for half a year, could you either merge it or request changes?