allow sessionFilesFolder to be relative to the workspace folder if th…

[Namyts]

…e path provided in the config is not absolute

Describe here what is this PR about and what we are achieving merging this.

Addresses #1254, and potentially helps with #1010

This PR aims allows the session file folder to be relative to the workspace if the path in the config is a relative path. Currently setting the session file folder to "./something" will cause it to create folder "/something" instead.

---

Thank you for your contribution! Before submitting this PR, please make sure:

• [x] Your code builds clean without any errors or warnings
• [x] You have made the needed changes to the docs
• [x] You have written a description of what is the purpose of this pull request above

[Namyts]

I really don't mind if it uses activeTextEditor instead. This is just a nice way to be able to sneak the generated file into the .vscode folder which is git ignored in my projects. Do you want me to change it?