lang: Replace the go-bindata usage with embed

This doesn't let us have nested mcl at the moment, but we could improve
on this with an embed API for each package. For now this makes building
the project easier.

lang/funcs/core/core.go

@@ -18,6 +18,9 @@
 package core
 
 import (
+	"embed"
+	"io/fs"
+
 	// import so the funcs register
 	_ "github.com/purpleidea/mgmt/lang/funcs/core/convert"
 	_ "github.com/purpleidea/mgmt/lang/funcs/core/datetime"
@@ -34,3 +37,34 @@ import (
 	_ "github.com/purpleidea/mgmt/lang/funcs/core/sys"
 	_ "github.com/purpleidea/mgmt/lang/funcs/core/world"
 )
+
+// TODO: Instead of doing this one-level embed, we could give each package an
+// API that it calls to "register" the private embed.FS that it wants to share.
+
+//go:embed */*.mcl
+var mcl embed.FS
+
+// AssetNames returns a flattened list of embedded .mcl file paths.
+func AssetNames() ([]string, error) {
+	fileSystem := mcl
+	paths := []string{}
+	err := fs.WalkDir(fileSystem, ".", func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() { // skip the dirs
+			return nil
+		}
+		paths = append(paths, path)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return paths, nil
+}
+
+// Asset returns the contents of an embedded .mcl file.
+func Asset(name string) ([]byte, error) {
+	return mcl.ReadFile(name)
+}