New API type: CurrentExecutingGoals.

[kaos]

Example use:

from pants.engine.goal import CurrentExecutingGoals

IsMyGoalRunning = bool

@rule
def check_my_goal_running(goals: CurrentExecutingGoals) -> IsMyGoalRunning:
    return goals.is_running(MyGoal.name)

@rule
def my_rule(..., my_goal_is_running: IsMyGoalRunning) -> MyResult:
  if my_goal_is_running:
    # conditional stuff for my-goal

  return MyResult()

Supersedes #17674.

[kaos]

@stuhood I think this API is prepared for the future where goals may run concurrently, even if the implementation to support it may differ.

[stuhood]

Thanks!