[Feature] Add convenient functions to return official codec in encoding package. about kratos

[kvii]

An example to describe package conflict.

"github.com/go-kratos/kratos/v2/encoding"
"github.com/go-kratos/kratos/v2/encoding/json"
encoding.GetCodec(json.Name)

"encoding/json" // has conflict
var _ json.RawMessage

[shenqidebaozi]

There doesn't seem to be any fundamental difference, but a list of functions has been added

[kvii]

Let's find some examples in standard library.

• slog.Info and `slog.Default().Info
• http.Get and http.DefaultClient.Get
• flag.Parse and flag.CommandLine.Parse
  ……

They are fundamentally the same, but they have been included in standard library.

[xchwan]

Is the YamlCodec() function in the example the one we need to write to simplify the GetCodec process?
it seems we need to have XmlCodec(), JsonCodec()....