This changes analyzer loading on Linux to be per user where before
clashes could occur in the temp directory.

This fix initially started out by making our temp directory logic more
robust. Essentially add per user sub directories, do extended permission
checks, etc ... That exacerbated a number of existing corner cases in
the code and forced us to put a lot more error handling into the
workspaces layer.

After discussion with the IDE team I decided to take the approach of
loading from a `Stream` on non-Windows platforms. The performance
difference is neglible (1ms to 2ms per assembly) and it removes the
overhead of copying them around on disk as well as the complexities that
come with managing the shadow copy directory.

This will be observable to any analyzer that used `Assembly.Location` as
it will now be `""`. That is only useful though for inspecting disks
which is already illegal for analyzers hence it's considered an
acceptable break.

closes dotnet#65415