ViewportAnnotation does not change if file size changes

[dpp-gerrit]

Steps to reproduce:

• Use a file that has one screen full of newlines
• Go to the top of the file and enter 10 newlines
• Notice that even though the file is now double the size, the viewport annotation on the remote site is still very large.

Reported by: coezbek

Original Ticket: dpp/bugs/207

[tobous]

Still present on the current master as of https://github.com/saros-project/saros/commit/2da87ac3bb0daf59c3ea2abdcbe5c2ced0d83608.

The issue only seems to be on the on the side that extends the file length. The remote participant updates the viewport annotation correctly.

Furthermore, the issue does not seem to have anything to do with the actual file size or initial viewport location. It can be reproduced with any initial file size or viewport location. The only important factor for this issue to happen is that a participant adds lines located in the current viewport of the other participant.

The issue resolves itself once the other participant changes their viewport.