MediaScrubProgressBar: Revert the remaining time computation hack

This merge request brings an adjustment to the remaining time computation with:

• The revert of the hack introduced in 3.5.9, it is no longer needed as we switched to libvlc 4.0.

This merge request also introduces a new property to the VLCPlaybackService:

• This helper retrieves the VLCTime object and avoids having to recreate it based on the mediaDuration int value to get the length of the currently playing media.

(Note: This merge request relies on: vlc!6056 (merged))

Closes #1818 (closed)