gpu/internal/convertshaders: move internal/cmd/convertshaders

The convert program is only used by the shaders from package gpu, and
we're about to make the backend package imported by the program internal
to package gpu. Move the converter below package gpu.

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

gpu/internal/convertshaders/workdir.go

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type WorkDir string
+
+func (wd WorkDir) Dir(path string) WorkDir {
+	dirname := filepath.Join(string(wd), path)
+	if err := os.Mkdir(dirname, 0755); err != nil {
+		if !os.IsExist(err) {
+			fmt.Fprintf(os.Stderr, "failed to create %q: %v\n", dirname, err)
+		}
+	}
+	return WorkDir(dirname)
+}
+
+func (wd WorkDir) Path(path ...string) (fullpath string) {
+	return filepath.Join(string(wd), strings.Join(path, "."))
+}
+
+func (wd WorkDir) WriteFile(path string, data []byte) error {
+	err := ioutil.WriteFile(path, data, 0644)
+	if err != nil {
+		return fmt.Errorf("unable to create %v: %w", path, err)
+	}
+	return nil
+}