Miscellaneous files not shown as misc

[dibarbet]

With the new file based program support, random .cs files opened in VSCode now show a project context of the file name, instead of 'Miscellaneous Files`

To repro, ensure you have the latest C# extension prerelease, then

1. Open a random .cs file
2. Wait for a while for the file to be loaded in a virtual project
3. Note how the active context changes to the file name instead of 'Miscellaneous Files'

While I definitely prefer 'Miscellaneous Files', I'm open to the idea that it could be the file name

[JoeRobich]

We might want to split this information up somehow.

The IsMiscellaneous property should likely have always been !HasAllInformation. This would be what the client uses to trigger the warning toast.
The Label being the filename for FBP makes sense. I do think the truly misc files should have the "Miscellaneous Files" text tho.

[RikkiGibson]

It should be fairly simple to adjust the project display name when the file is modified, based on whether we think it is a file-based program.

Note that the result of this can be that adding/removing a loose ; from the top of the file, can cause us to rename the file between app (net10.0) and Miscellaneous Files. This doesn't strike me as a problem, though.