Prevent CargoCleanTask & RustUpTargetAddTask from running in parallel

An error occurs when multiple cargoClean tasks that clean the same workspace run in parallel. This PR fixes that issue using a global lock as in RustUpTargetAddTask.

Changes

• Added GloballyLockedTask. GloballyLockedTask.globalLock takes an identifier string and a code block and executes the code block while other code blocks with the same identifier are suspended.
• Made CargoCleanTask and RustUpTargetAddTask use GloballyLockedTask.
  • CargoCleanTask does not block another CargoCleanTask if it cleans a different workspace.
  • RustUpTargetAddTask blocks every other RustUpTargetAddTask. For some reason, sometimes simultaneous rustup target add commands fail even when they're installing different triples.