[Feature Request] Make 'Workspace as folder' available for plugins through NPPM_ message

[webketje]

Description of the feature request

It would be great to be able to access the path of the currently opened 'folder as workspace' (e.g. NPPM_GETFOLDERASWORKSPACE) for plugins like pythonscript and NppExec, similar to NPPM_GETPLUGINSCONFIGDIR defined in Notepad_plus_msgs.h

Motivation

In many other editors, folder as workspace sets the default current directory. This can be an important path marker for scripts like npm run <task> (JS) or php artisan <cmd> (PHP Laravel) or other build scripts/ tasks that require to be executed from a project root path to work as intended.

[webketje]

And it would be even cooler if the 'folder as workspace' saved the folder to session.xml when Save session is clicked, and automatically setFolderAsWorkspace with the path value from session.xml.