Shorten the "temp" path used for the miscellaneous files project used in the Razor language server

[DustinCampbell]

In the Razor language server, a miscellaneous files project is added with a fake-but-unique file path that looks like so:

var tempDirectory = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("n"));
var filePath = Path.Combine(tempDirectory, "__MISC_RAZOR_PROJECT__"); 

It would be helpful to shorten this path or make it more obvious for scanning through logs.

see #11295 (comment)

[davidwengier]

Since we use fancy interpolated string handlers for logging, we could potentially add an AppendFormatted(ProjectKey key) method to our handler, and log a special value, rather than have to deal with potential fallout from changing the misc files path itself, in any meaningful way