This is used when calling click_message_action_mobile to wait
for the message actions menu to finish animating up before
attempting to click on it using capybara. Without this, in
the time between capybara getting the x,y position of a menu
item to click on and the click being fired, the animating menu
can move that item out of the way.
With the new helper, we constantly compare x,y client rect positions
for the animating element and wait for them to stabilise. Once they
do, it means the animation is done, and it is safe to click on
anything within the element.
Re-enables mobile system specs for chat that were ignored because
of this.
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