Load built-in plugins for kustomize localize (#4869)

* Load and filter built-in plugins

* Improve readability

* Process plugins as resources instead of bytes

* Throw error for validators

* Differentiate generators, transformers processing

* Enable validators

* add wrapper error
* improve documentation

api/internal/localizer/builtinplugins.go

@@ -0,0 +1,38 @@
+// Copyright 2022 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package localizer
+
+import (
+	"sigs.k8s.io/kustomize/kyaml/kio"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+// localizeBuiltinGenerators localizes built-in generators with file paths.
+// Note that this excludes helm, which needs a repo.
+type localizeBuiltinGenerators struct {
+}
+
+var _ kio.Filter = &localizeBuiltinGenerators{}
+
+// Filter localizes the built-in generators with file paths. Filter returns an error if
+// generators contains a resource that is not a built-in generator, cannot contain a file path,
+// needs more than a file path like helm, or is not localizable.
+// TODO(annasong): implement
+func (lbg *localizeBuiltinGenerators) Filter(generators []*yaml.RNode) ([]*yaml.RNode, error) {
+	return generators, nil
+}
+
+// localizeBuiltinTransformers localizes built-in transformers with file paths.
+type localizeBuiltinTransformers struct {
+}
+
+var _ kio.Filter = &localizeBuiltinTransformers{}
+
+// Filter localizes the built-in transformers with file paths. Filter returns an error if
+// transformers contains a resource that is not a built-in transformer, cannot contain a file path,
+// or is not localizable.
+// TODO(annasong): implement
+func (lbt *localizeBuiltinTransformers) Filter(transformers []*yaml.RNode) ([]*yaml.RNode, error) {
+	return transformers, nil
+}