the slider on the touch bar was always updated when any of the related
properties changed their value. this is partially dependent on the
refresh rate of the video, in the case of time-pos. too many updates to
touch bar impact the render performance.
to prevent this we only update the slider when necessary, when the touch
bar or the touch bar item is visible. the touch bar items only need a
granularity of seconds without any decimals, but the time-pos property
provides a granularity with decimals. we floor those values and only
update the touch bar items when we have at least a 1 second difference.
we also check for the visibility of the touch bar and its items.
Fixes#8477
the NSSliderTouchBarItem seem to be broken in a way it can't be fixed.
it has constraints set by default that can't be removed and lead to
warnings and render performance regressions.
instead of using the preconfigured NSSliderTouchBarItem we use a custom
touch bar item (NSCustomTouchBarItem) with a slider, which essential are
the same. this way we can configure our constraints ourselves, which
aren't needed in the first place.
Fixes: #7047
