kindsys: Fix CUE code generation on Windows (#62812)

* fix Windows paths

* fix remaining paths issues

* clean up multiple use of Dir()

* fix headers in generated files

pkg/plugins/pfs/decl_parser.go

@@ -33,7 +33,7 @@ func (psr *declParser) Parse(root fs.FS) ([]*PluginDecl, error) {
 
 	decls := make([]*PluginDecl, 0)
 	for _, plugin := range plugins {
-		path := filepath.Dir(plugin)
+		path := filepath.ToSlash(filepath.Dir(plugin))
 		base := filepath.Base(path)
 		if skip, ok := psr.skip[base]; ok && skip {
 			continue

pkg/plugins/pfs/pfs.go

@@ -235,7 +235,7 @@ func ParsePluginFS(fsys fs.FS, rt *thema.Runtime) (ParsedPlugin, error) {
 }
 
 func ensureCueMod(fsys fs.FS, pdef plugindef.PluginDef) (fs.FS, error) {
-	if modf, err := fs.ReadFile(fsys, filepath.Join("cue.mod", "module.cue")); err != nil {
+	if modf, err := fs.ReadFile(fsys, "cue.mod/module.cue"); err != nil {
 		if !errors.Is(err, fs.ErrNotExist) {
 			return nil, err
 		}