[feat] Implement xdg projects directory

[PopLamina]

Describe the problem

The projects directory is currently stored in a sub directory in the Documents folder on Linux instead of the recently added xdg projects directory

Describe the solution you'd like

The projects directory should be relocated on Linux from ~/Documents/Phoenix Code to the xdg standard projects directory location $XDG_PROJECTS_DIR/Phoenix Code (~/Projects/Phoenix Code)

Alternatives considered

An alternative option would be to let the end user customise the location of their projects directory allowing them to set it to the standard xdg directory or elsewhere

Additional context

No response

[abose]

Thanks for reporting this issue. Will check what to do here as this will break exiting users who already have it there.