Players: Adjust Video Player's constraints + Sliders improvements

This merge request is a follow-up from !1106 (closed) with @caro's contribution that introduced:

• Constraints adjustments to the Video Player's navigation bar and the controls.

This merge request also brings additional improvements such as:

• The brightness and volume sliders' constraints that are now aligned to the scrub progress bar and the player controls of the Video Player.
• The Audio Player's brightness and volume sliders now have additional padding to match the constraints adjustments and visual improvements.

Here are some screenshots with and without color backgrounds in order to better visualize the Video Player's constraints:

Here is a screenshot of the Audio Player's interface when both sliders are visible:

changed milestone to %3.5.0

added Maintenance Player labels

changed the description

approved this merge request

Looks great to me!

@caro do you have an opinion?

sorry for the late reply. One thing that I just saw is that there is constraints code in layoutsubviews. I would move that somewhere else because that can get called more than once and there is more context in this StackOverflow: https://stackoverflow.com/questions/49742280/ios-adding-new-constraints-in-a-custom-view-the-rely-on-the-views-frame otherwise looks good to me :)

added 43 commits

• ab3dbd75...5700d587 - 40 commits from branch videolan:master
• ed3b79c2 - Video Player: adjust constraints
• 81d5c712 - VideoPlayerViewController: Adjust the constraints
• 134a6e7a - AudioPlayerView: Add padding to the sliders

Compare with previous version

resolved all threads

added 9 commits

• 134a6e7a...457f18a7 - 6 commits from branch videolan:master
• 6aa53d3e - Video Player: adjust constraints
• c8fa01a8 - VideoPlayerViewController: Adjust the constraints
• 99af07cd - AudioPlayerView: Add padding to the sliders

Compare with previous version

enabled an automatic merge when the pipeline for 99af07cd succeeds

merged