Allow to pass in semaphores to wait for before executing
and to signal after executing the command buffer. This
just exposes the capabilities of the underlying Vulkan
api. Update all callers to pass no semaphores, for now.
We will use this in the future.
One cannot use #if...#endif within macro calls in Visual Studio and
possibly other compilers, and there are more uses of VLAs that need to be
replaced with g_newa().
There were also checks for the clip type in gskvulkanrenderpass.c which
were possibly not done right (using the address of the type value to check
for a type value), which triggered errors as one is attempting to compare
a pointer type to an enum/int type.
https://bugzilla.gnome.org/show_bug.cgi?id=773299
This way we can pass the command pool around.
And that allows us to allocate and submitcustom buffers.
And that is necessary to make staging images work.
