Changes to SmartSemicolonHandler:
- Use text edits rather than a semantic update to insert a tag number, to avoid
  duplication of surrounding whitespace.
- Correctly determine the next tag number within a message containing groups.
- Detect and update a next-tag-number comment located at the end of a message.

Change-Id: Ie8967f3393ef6f9b2e1fbb0118916f7e82c8f8a0