Scrolling in RTC session difficult when cell updates

[asteppke]

With the current jupyter-collaboration 2.1.0 (and earlier) and jupyter lab 4.18 scrolling through the notebook becomes very difficult if there is a cell running with a lot of output in the "primary" jupyter lab.

To reproduce in a new notebook create the following example cell:

import time
for i in range(100_000_000):
    print(f"{i}, ", end="")
    time.sleep(0.05)

and open the notebook in a collaborative session in a second window / computer.

If the cursor is at the end of the notebook scrolling is nearly impossible. If the cell is collapsed the scroll bar jumps as in the following screencast:

The user interface in the "primary" jupyter lab that executed the cell shows no issues.

This looks very similar to #310, only that the collapsing of the cell gets temporarily reversed.

[davidbrochart]

cc @afshin