video_output: place regions in the whole display area
To be able to put subtitles in black bars we need to put subpicture regions anywhere inside the display, not just the area where the video is. Now the placement of subpicture regions is given in display coordinates, regardless of where the video is. The display is supposed to put the video exactly where the core intends it to be, otherwise absolute subpicture placement would be broken.
Draft on top of !5113 (merged), only the 5 last commits are new.
Untested on: libplacebo, xcb, android.
Working on VLCSampleBufferDisplay
as long as !4993 (merged) is applied.
This MR is the fourth part of !5036 (merged)
Edited by Steve Lhomme