We were mimicking Firefox' behavior that whenever a programmatic change
to an <input>'s or <textarea>'s selection happened, the new selection
focus is brought into view by scrolling. Currently we run a layout
update synchronously for that to make sure we have the fragment's
correct dimensions, which caused a significant performance regression in
Speedometer.
Since this is non-standard behavior, let's mimic Chromium instead which
does not scroll at all - only for direct user initiated input such as
typing.
Relevant issues:
* https://github.com/whatwg/html/issues/6217
* https://bugzilla.mozilla.org/show_bug.cgi?id=232405
* https://issues.chromium.org/issues/41081857
