app,gpu,internal/vk: add Vulkan port for Wayland, X11, Android

This change implements a Vulkan port for the two renderers, old and
compute. Run with GIORENDERER=forcecompute to test the compute renderer.

To shake out bugs faster, it is also made the default on systems that
support it. To disable Vulkan and force the use of OpenGL, use the
`novulkan` tag:

$ go run -tags novulkan gioui.org/example/kitchen

Don't forget to file an issue describing the issue that prompted the use
of the tag.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/internal/driver/api.go

@@ -31,6 +31,17 @@ type MetalRenderTarget struct {
 	Texture unsafe.Pointer
 }
 
+type VulkanRenderTarget struct {
+	// WaitSem is a VkSemaphore that must signaled before accessing Framebuffer.
+	WaitSem uint64
+	// SignalSem is a VkSemaphore that signal access to Framebuffer is complete.
+	SignalSem uint64
+	// Image is the VkImage to render into.
+	Image uint64
+	// Framebuffer is a VkFramebuffer for Image.
+	Framebuffer uint64
+}
+
 type OpenGL struct {
 	// ES forces the use of ANGLE OpenGL ES libraries on macOS. It is
 	// ignored on all other platforms.
@@ -55,11 +66,25 @@ type Metal struct {
 	PixelFormat int
 }
 
+type Vulkan struct {
+	// PhysDevice is a VkPhysicalDevice.
+	PhysDevice unsafe.Pointer
+	// Device is a VkDevice.
+	Device unsafe.Pointer
+	// QueueFamily is the queue familily index of the queue.
+	QueueFamily int
+	// QueueIndex is the logical queue index of the queue.
+	QueueIndex int
+	// Format is a VkFormat that matches render targets.
+	Format int
+}
+
 // API specific device constructors.
 var (
 	NewOpenGLDevice     func(api OpenGL) (Device, error)
 	NewDirect3D11Device func(api Direct3D11) (Device, error)
 	NewMetalDevice      func(api Metal) (Device, error)
+	NewVulkanDevice     func(api Vulkan) (Device, error)
 )
 
 // NewDevice creates a new Device given the api.
@@ -81,6 +106,10 @@ func NewDevice(api API) (Device, error) {
 		if NewMetalDevice != nil {
 			return NewMetalDevice(api)
 		}
+	case Vulkan:
+		if NewVulkanDevice != nil {
+			return NewVulkanDevice(api)
+		}
 	}
 	return nil, fmt.Errorf("driver: no driver available for the API %T", api)
 }
@@ -88,6 +117,8 @@ func NewDevice(api API) (Device, error) {
 func (OpenGL) implementsAPI()                          {}
 func (Direct3D11) implementsAPI()                      {}
 func (Metal) implementsAPI()                           {}
+func (Vulkan) implementsAPI()                          {}
 func (OpenGLRenderTarget) ImplementsRenderTarget()     {}
 func (Direct3D11RenderTarget) ImplementsRenderTarget() {}
 func (MetalRenderTarget) ImplementsRenderTarget()      {}
+func (VulkanRenderTarget) ImplementsRenderTarget()     {}