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: