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/errors.go

@@ -0,0 +1,18 @@
+// Copyright 2022 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package localizer
+
+import "fmt"
+
+type ResourceLoadError struct {
+	InlineError error
+	FileError   error
+}
+
+var _ error = ResourceLoadError{}
+
+func (rle ResourceLoadError) Error() string {
+	return fmt.Sprintf(`when parsing as inline received error: %s
+when parsing as filepath received error: %s`, rle.InlineError, rle.FileError)
+}