Follow cl-gfx f9bc46d: usage types, the default backend, frame numbers
open-device's :backend defaults to :vulkan, and *default-backend* is
gone. buffer-usage, texture-usage and validation-severity are types,
and a usage of neither is a type-error. Backends signal cl-gfx's
conditions with signal-gfx-error and signal-unsupported-error; the core
numbers frames, and frame-number and command-list-count have no
writers.
Follow cl-gfx 02db471: Vulkan 1.4, its features, and surfaces destroyed at once
A device needs Vulkan 1.4, whose devices have every feature cl-gfx
enables on all: the optional features are :GEOMETRY-SHADERS,
:TESSELLATION-SHADERS, :FLOAT64, :MULTISAMPLE-STORAGE-TEXTURES and
:VERTEX-STORES, and cube arrays and anisotropic samplers need none. A
multisampled texture may be a :2D-ARRAY, and DESTROY-SURFACE waits for
the GPU and destroys the surface at once, between frames.
