Support cancellation on plugin file events

[msujew]

What it does

Closes #11508
Closes #11563

Supersedes the PR above by adapting the approach taken by vscode. vscode always passes the token into the async event, so we don't have to do that ourselves for each event.

Additionally enables to actually cancel the file events using a notification similar to vscode.

Also updates a few missing localizable strings in the file-service.ts file.

How to test

1. Install the test extension cancellation-token-0.0.1.vsix.
2. Create a new file in the explorer.
3. A notification should appear that a file is in progress of being created (both from Theia and from the extension)
4. Cancelling the operation explicitly or by waiting (5 seconds by default) will cancel the token and another notification will appear that the operation has been cancelled. The file will then be successfully created.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

I confirm that the changes look good, and work as expected 👍