Make identity server work with publish single file in .NET 5.0

[javiercn]

What issue does this PR address?
#4810

Does this PR introduce a breaking change?
No

Please check if the PR fulfills these requirements

• The commit follows our guidelines
• Unit Tests for the changes have been added (for bug fixes / features)
  I couldn't find unit tests in the area testing the current behavior, I'm happy to add one if you point me where to do so.

Other information:
Manual validation of the changes.

[leastprivilege]

thanks!

[brockallen]

Was this change backwards compat w/ 3.1?

[javiercn]

@brockallen it should, but this is not an issue in 3.1 since the publish single file strategy is different (the assemblies we packaged and unzipped on a temp directory, while now they are mapped directly into memory, so there's no physical file at all, which was the root cause of the issue).

In general, is not "safe" to use Assembly.Location AFAIK if you want to support publish single file, we had to do work in MVC too to avoid issues there too.

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.