dvdnav: use the dvd playtime as PCR

Using the PS SCR value as a PCR isn't correct in the DVD use case. DVDs are made of multiple non-continuous PS streams that aren't constrained to have a consistent SCR across streams. Basically, each VOB changes might trigger a PCR reset. This was fine in VLC 3, but now the PCR is used to drive the clock and the seek bar which leads to hazardous behaviors, the most noticeable now is the seekbar incorrect timestamps.

This patch uses the DVD playtime as the PCR and adapts the DTS instead. This ensure a continuous PCR curve even on VOB changes.