Add GitHub Action to build .NET MAUI playground

[jfversluis]

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We should add a GitHub action that build the .NET MAUI playground project (excluded right now) so that we test that code as well as the .NET MAUI workload restore script.

Also see: #12284 (comment)

[maddymontaquila]

This has been implemented in #12284. Closing as resolved. Thank you for the proposal! If you have follow-up feature requests, please open a new issue.

[davidfowl]

Reopening after reviewing the recent bulk closure. The close comment appears to cite work that does not fully address this issue, so this should remain open for normal triage.