Fix issues with package management subdirectories

[KevinRansom]

Fixes #12140 - Fsc deletes the output directory
Fixes #11923 - FSI fails with "error FS3217: No such file or directory"

Additionally, this makes working directory evaluation lazy ... so it doesn't touch the disk unless nuget evaluation is actually required.

#12140 - Fsc deletes the output directory
The output directory deletion was because, we pass the directory from --out: to the package manager, the pm intended to create use and delete a subdirectory from that, however, due to a bug it didn't. Instead it used the directory from --out: and tried to delete that.

Fixes #11923 - FSI fails with "error FS3217: No such file or directory"
This failed because when no directory is specified the package manager created a directory in the temp directory named nuget/Some randomized directory name.

On linux, if the tempdir/nuget had been created by a different user, e.g. the sudo admin user, then subsequent scri0pts not run with that user would fail.

This modification simply eliminates the common part of the path. So the script should be able to write using whatever user is executing the code.

[brettfo]

Don't you only want to delete the directory if line 198 above (Directory.CreateDirectory(directory) |> ignore) was executed, not simply if the lazy block was entered?

[KevinRansom]

@brettfo , I think the real issue, is that the directory must be created. If a directory with the name already exists, then it's still a problem. Of course, given that the directory name is 'managed threadid - some randomly generated guid' then it's unlikely to already exist. But I shall address that.