detach workspace-d initialization from activePlugin call

[WebFreak001]

workspace-d should only initialize when there is either

• a dub.json/dub.sdl in the project root (or package.json looking like dub package)
• a command ran requiring workspace-d
• settings contain fsworkspace additional import paths & project is not a dub project / dub is disabled

basically just lazy load it when its required or the open folder is guaranteed a dub project. Initialization of single files and non-dub projects is quick anyway.

Some code-d commands not using workspace-d have long startup times otherwise