macOS: Log view: Fix autoscroll to end of log

macOS: Log view: Fix autoscroll to end of log

Looks like the tableview doesn't know how much to scroll to get to the
end when we use usesAutomaticRowHeights. So we wait for the tableview
to realize its frame has changed and then scroll to the bottom of the
frame explicitly.

Also, we keep track of whether the scroll view is scrolled to the end or
not every time scrolling happens, not just when we add log entries to
the table.

Signed-off-by: Roopesh Chander <roop@roopc.net>