Refine UX of H264 bitrate slider (in Video Settings dialog)

In the video settings dialog, the slider for adjusting the H264 bitrate has a step size of 50, and a value range of 50–20.000, resulting in 400 slider steps.

That UX can be improved, though, because while it makes sense to fine-tune the bitrate value at the lower end of the scale (e.g. if users are tight on bandwidth), a course-grained step size is sufficient on the upper end of the scale (e.g. the difference between 18200 and 18250 doesn’t matter as much).

Therefore, the slider could better behave logarithmically, i.e. with a continuously increasing step size across the value range. For example with a step size of 25 at the lower end, and a step size of 500 at the upper end. See video demo below, taken from a “quick-and-dirty” mock implementation:

https://user-images.githubusercontent.com/83721279/199057531-31251632-bf71-4d38-b793-03559fda7f80.mov

Start at the video settings dialog and review the existing H264 bitrate slider, then compare its behavior with the linked quick-and-dirty mock implementation. Done means the slider uses continuously increasing steps across the 50–20,000 range, with fine adjustments near the lower end and coarser adjustments near the upper end.