[Enhancement] Support Jack-in without file open for single-rooted workspace

[cfehse]

The extension should support the a Jack-in process to be started without an open file in a single-rooted workspace environment (e.g. opened via Open Folder...). Under these conditions the project file can be reliably detected even without an open file.
This can not be done in an multi-rooted workspace - at least not until vscode provides an API to get any selected folder in the explorer view. Here a file must be opened farther to be able to detect the root folder of the project.

[cfehse]

This is fixed in version 2.0.47.