Document whether FileExtensionContentTypeProvider is thread-safe

[mattflaschen]

Please document whether FileExtensionContentTypeProvider is thread-safe. If so, it can be used as a singleton.

Software versions

Check the .NET target framework(s) being used, and include the version number(s).

• .NET Core
• .NET 5.0 or later (8.0)
• .NET Framework
• .NET Standard

[guardrex]

Hello @mattflaschen ... Please close this issue and open a new issue from THIS LINK, which will add the correct metadata to the issue and automatically ping the author. That link is the "Open a documentation issue" link from the bottom of the Fundamentals > Static files article, where this API is covered.