Allow tasks to be run via terminal suggest

[Tyriar]

Chatting with @meganrogge, we should just add all tasks to terminal suggest. Instead of doing something clever, trying to light up a task in a non-task terminal, this could literally just run that particular task. So If the user types "build", have it show up as an option:

As for priority, my intuition says they should show low in the list because it's special in that it's not running a command. However in the example screenshot above we probably actually want such tasks to be positioned just below the .\.build\ suggestion.

Some other things to consider:

• Task labels often include spaces, so should they show up when you type "vs code build"?
• If a user types npm run watch, should npm tasks that include watch in their script name, not their label be included here?
  
• Behind the scenes, this could be implemented via a new internal completion item kind that runs a vscode command.
• Should these live as a new completion item provider implemented inside task/?
• These items should use the task's tools icon