Avoid blocking the pipeline while handling refreshLocal during document lifecycle events

[testforstephen]

This is a follow-up on #2518 (comment).

As shown in the callstack below, the default refreshLocal implementation uses two locks: a scheduling rule for jobmanager concurrency and a workspace lock for workspace tree modification. The workspace lock is essential to prevent the workspace tree from being corrupted during refresh. We can try setting the scheduling rule to null for refreshLocal in documentLifecycleHandler, since it only refreshes the current Java file and has a limited scope. I tested the new refresh approach with use cases such as creating, renaming and saving a Java file, it works fine.

- Call Stack:
File.refreshLocal(int,IProgressMonitor) File.class:316
Resource.refreshLocal(int,IProgressMonitor) Resource.class:1565
Workspace.prepareOperation(ISchedulingRule,IProgressMonitor)  Workspace.class:2332
WorkManager.checkIn(ISchedulingRule,IProgressMonitor) WorkManager.class:124

- Locks used in refresh operation:
/**
	 * An operation calls this method and it only returns when the operation is
	 * free to run.
	 */
	public void checkIn(ISchedulingRule rule, IProgressMonitor monitor) throws CoreException {
		boolean success = false;
		try {
			if (workspace.isTreeLocked()) {
				String msg = Messages.resources_cannotModify;
				throw new ResourceException(IResourceStatus.WORKSPACE_LOCKED, null, msg, null);
			}
			jobManager.beginRule(rule, monitor);   // scheduling rule check
			lock.acquire();   // workspace lock check
			incrementPreparedOperations();
			success = true;
		} finally {
			//remember if we failed to check in, so we can avoid check out
			if (!success)
				checkInFailed.set(Boolean.TRUE);
		}
	}

[jdneo]

LGTM

According to the implementation,

jobManager.beginRule(rule, monitor);   // scheduling rule check
lock.acquire();   // workspace lock check

Though jobManager.beginRule(rule, monitor); becomes non-blocking, lock.acquire(); will still block multiple requests. So, it should be safe.