Fix race condition in Add-Type

[daxian-dbw]

PR Summary

Fix #19470

Add-Type uses static HashSet and Dictionary for caching type names and assemblies, which are not thread-safe. When running Add-Type with the same C# code from multiple Runspaces simultaneously, these caches may be accessed at the same time, and that will cause a race condition.

The fix is to use ConcurrentDictionary for both caches.

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[SeeminglyScience]

LGTM!

[ghost]

🎉v7.4.0-preview.3 has been released which incorporates this pull request.:tada:

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