internal/d3d11: extract Direct3D API to separate package

We're about the merge the Direct3D backend into package gpu. Extract the
raw Direct3D API to its own package, just like package glimpl.

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

app/headless/headless_windows.go

@@ -6,7 +6,9 @@ import (
 	"unsafe"
 
 	"gioui.org/gpu"
-	"gioui.org/app/internal/d3d11"
+	"gioui.org/internal/d3d11"
+
+	_ "gioui.org/app/internal/d3d11"
 )
 
 type d3d11Context struct {
@@ -14,15 +16,20 @@ type d3d11Context struct {
 }
 
 func newContext() (context, error) {
-	dev, err := d3d11.NewDevice()
+	dev, ctx, _, err := d3d11.CreateDevice(
+		d3d11.DRIVER_TYPE_HARDWARE,
+		0,
+	)
 	if err != nil {
 		return nil, err
 	}
+	// Don't need it.
+	d3d11.IUnknownRelease(unsafe.Pointer(ctx), ctx.Vtbl.Release)
 	return &d3d11Context{dev: dev}, nil
 }
 
 func (c *d3d11Context) API() gpu.API {
-	return gpu.Direct3D11{Device: unsafe.Pointer(c.dev.Handle)}
+	return gpu.Direct3D11{Device: unsafe.Pointer(c.dev)}
 }
 
 func (c *d3d11Context) MakeCurrent() error {
@@ -33,6 +40,6 @@ func (c *d3d11Context) ReleaseCurrent() {
 }
 
 func (c *d3d11Context) Release() {
-	c.dev.Release()
+	d3d11.IUnknownRelease(unsafe.Pointer(c.dev), c.dev.Vtbl.Release)
 	c.dev = nil
 }