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