Configure Prusti arguments and environment variables

[fpoli]

In this PR:

• Add configuration options to let the user specify extra arguments and environment variables to be used when running prusti-rustc, cargo-prusti and prusti-server. This mitigates Allow configuring the server #62.
• Make the prusti-server start in the first folder of the workspace. This way, if the user enables PRUSTI_DUMP_VIPER_PROGRAM, the dump will end up in the workspace and not in some obscure folder of VS Code.

I haven't added a way to test that the new configuration options work as intended. I just tested them locally.

[JonasAlaif]

Again, we could move the --port setting to extraPrustiServerArgs instead of hardcoding it?

[fpoli]

Do you see a use case for letting the user choose the port?

[JonasAlaif]

Not really, but I don't see much of a reason for the --port setting in the first place aha

[fpoli]

Yeah :D We could at least make 0 the default.

[JonasAlaif]

Makes sense, in that case we can merge as is

[fpoli]

Mmm, for some reason the prusti-server keeps failing on Windows.

[JonasAlaif]

When I run the test on Windows I get:

Prusti server will be executed in '/C:/Users/Jonas/AppData/Local/Temp/tmp-8312-lLQef3cvi7GF'
[Prusti server] Start "c:\Users\Jonas\AppData\Roaming\Code\User\globalStorage\viper-admin.prusti-assistant\prustiTools\LatestDev\prusti\prusti-server.exe --port 0"
[Prusti server] Mark server as "Running".
[Prusti server] Server process error: Error: spawn c:\Users\Jonas\AppData\Roaming\Code\User\globalStorage\viper-admin.prusti-assistant\prustiTools\LatestDev\prusti\prusti-server.exe ENOENT

As the output in Prusti Assistant Trace. It would be nice to display this output in the CI

[JonasAlaif]

I think that the error is caused by the leading / in /C:/Users/Jonas/AppData/Local/Temp/tmp-8312-lLQef3cvi7GF

[fpoli]

I think that the error is caused by the leading / in /C:/Users/Jonas/AppData/Local/Temp/tmp-8312-lLQef3cvi7GF

Thanks! Apparently, for disk operations one must use Uri::fsPath instead of Uri::path.

I added plenty of log to the console. Debugging should be easier.

[JonasAlaif]

Hahaha, this github CI on all 3 platforms is invaluable