The path to the MoltenVK library can be specified by the
LIBMOLTENVK_PATH environment variable, otherwise it assumes it is
located in the application bundle's Contents/MacOS directory.
The current approach results in the UI thread creating a graphics device
whilst the core is running, leading to races on function pointers, and
potentially crashing.
Given this is a base class, we should clearly state what the parameters
to the functions in its exposed interface actually mean or represent.
This avoids needing to hunt for the definition of the functions in cpp
files.
While we're at it, normalize said parameter names so they follow our
naming guidelines.
Given that this only contains functions from the VideoBackendBase class,
it makes more sense to move these to the relevant cpp file to keep them
all together.
There's no official implementation of the Vulkan API,
and Dolphin currently isn't set-up to work with the
single, commercially-available third-party implementation.
