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/plugindef/gen.go

@@ -10,7 +10,6 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"strings"
 
 	"cuelang.org/go/cue/cuecontext"
 	"github.com/dave/dst"
@@ -40,8 +39,8 @@ func main() {
 		fmt.Fprintf(os.Stderr, "could not get working directory: %s", err)
 		os.Exit(1)
 	}
-	grootp := strings.Split(cwd, string(os.PathSeparator))
-	groot := filepath.Join(string(os.PathSeparator), filepath.Join(grootp[:len(grootp)-3]...))
+
+	groot := filepath.Clean(filepath.Join(cwd, "../../.."))
 
 	jfs := elsedie(jl.GenerateFS(lin))("plugindef jenny pipeline failed")
 	if _, set := os.LookupEnv("CODEGEN_VERIFY"); set {