Niklas Haas authored Oct 01, 2018 and Thomas Guillem committed Nov 07, 2018

This uses libplacebo's rendering helpers for all video output, on top of
the vulkan graphics API. Some notes:

- The existing fourcc/chroma helpers don't really line up with what the
  libplacebo API expects, or in some cases return values that just don't
  seem to make sense. I was advised against touching them for fear of
  breaking the rest of VLC - so we add our own helpers that give us the
  information in the format we need for libplacebo.

- Not all libplacebo options are mapped. There's no ability to create
  custom filter functions (which libplacebo/mpv support), and there's
  also no support for ICC profiles / 3DLUTs (which libplacebo supports)
  nor for the new color blindness simulation parameters in libplacebo
  v0.6. We also don't map the VLC brightness/hue/gamma/etc. options to
  the libplacebo structs - we could do it for free as part of the video
  decode matrix, rather than needing to insert a CPU filter for it.

- How to create the vulkan surface will depend on the platform (much
  like in opengl), so we move context, surface and device creation into
  a single module (`vulkan/surface.c`) which will be conditionally
  compiled depending on the platform in order to provide support for
  multiple surfaces side-by-side (e.g. x11 and wayland). This does mean
  that the context/device-related options end up being separate per
  platform, but OTOH this is not that bad since different platforms
  might want different e.g. swapchain modes (an example being wayland,
  which can make better use of mailbox rather than fifo).

- libplacebo doesn't have a "configure" step, instead all rendering
  parameters are fully dynamic. So we could call UpdateParams() in our
  module at any point in time when the config values change.
  Unfortunately, there's no easy way for us to find out when this is the
  case, so right now changing the vulkan module options requires a
  module reinit to take effect. In theory we could change this. (As an
  aside: calling var_Inherit* per frame does work to get us the changes
  in "realtime", as soon as the user clicks "save", but this may block
  for arbitrary amounts of time so I was advised against doing it)

Due to the new functions, structs and enum members used, the minimum
libplacebo version has been bumped up to v0.5.0. In theory we could also
try and support v0.4.0 with some #ifdefs, but v0.5.0 has been out for
several months now so it should be a safe requirement.