Alter CI to run Rich Navigation, add new Rich Nav specific pipeline

[jepetty]

I've altered two files:

1. Add a Rich Navigation specific build (which will appear as a new build pipeline), indexing on every push to master. This will allow you to use Rich Navigation in Visual Studio to enable cross-repository searches, serverless navigation at https://online.visualstudio.com/github/dotnet/msbuild, and integrated GitHub C# navigation once that is released (or, comment below if you want to be added to the preview now 😊).
2. Added the Rich Navigation task to your normal CI. This has all the same benefits of ^, but also indexes your pull requests for a richer code review experience. This does come at the cost of increasing the time of your CI.

Based on your team's preference, only one of these changes is necessary.

Rich Code Navigation

Docs Link
With Rich Code Navigation, you can use editor-level navigation capabilities (like peek definition, find all references, and even diagnostics) on a pull request, without requiring a local checkout. This is available across all files and dependencies of your repository.

Rich Code Navigation is available for Visual Studio (for repos hosted on GitHub or Azure Repos) and Visual Studio Code (for repos hosted on GitHub).

Rich Code Navigation supports these capabilities:

• Hover
• Peek definition and Go to definition
• Peek references and Find all references
• Go to type definition
• Go to implementation
• Diagnostics

[roji]

and integrated GitHub C# navigation once that is released (or, comment below if you want to be added to the preview now blush).

Am personally definitely interested in this 😃

[jepetty]

Please ignore my latest hack-tacular commit replacing the normal CI with the Rich Nav pipeline. I'm doing this purely for testing purposes and will undo the changes once I've verified the pipeline runs successfully

[jepetty]

I've removed my hack-tacular commit to replace the normal CI, but not before verifying the rich nav pipeline will run correctly: https://dev.azure.com/dnceng/public/_build/results?buildId=860052&view=logs&j=0bc77094-9fcd-5c38-f6e4-27d2ae131589&t=0bc77094-9fcd-5c38-f6e4-27d2ae131589. This PR is good to merge, then I'll create a new pipeline in dnceng

[dougbu]

@smitpatel I defer to you on whether the EF Core team needs or wants the extra clickability in PRs. If not, merge away 😺