Remember the cwd for plugins

[rwols]

Resolves #1788

[rwols]

@randy3k for some reason the macOS workflow cannot install package control?

[jwortmann]

Thanks! Despite what I wrote in the linked issue, I think it should be possible for my usecase to derive the desired environment even with the actual working directory, i.e. workspace_folders[0].path or os.getcwd() if the on_pre_start result is None (the only thing I have to do is to check whether a corresponding metadata file exists in the directory). So if you think that it would be more useful to store the actual working directory, I guess that should be fine too.

[rwols]

So if you think that it would be more useful to store the actual working directory, I guess that should be fine too.

I think the current diff will do fine :)