es_out: shift with the main source normal time

This fixes synchronization issues when 2 demuxers have a different time base (like .ts + .srt for example).

Ideally, we should also subtract the slave normal time but there is no way to fetch it for now, indeed es_out_SetTimes should be called directly from demuxers modules and not from input/input.c.

Fixes #21999 (closed)