Improve performance on multiple versions (#13573)

Existing:

```go
type xlMetaV2 struct {
    Versions []xlMetaV2Version `json:"Versions" msg:"Versions"`
}
```

Serialized as regular MessagePack.

```go
//msgp:tuple xlMetaV2VersionHeader
type xlMetaV2VersionHeader struct {
	VersionID [16]byte
	ModTime   int64
	Type      VersionType
	Flags     xlFlags
}
```

Serialize as streaming MessagePack, format:

```
int(headerVersion)
int(xlmetaVersion)
int(nVersions)
for each version {
    binary blob, xlMetaV2VersionHeader, serialized
    binary blob, xlMetaV2Version, serialized.
}
```

xlMetaV2VersionHeader is <= 30 bytes serialized. Deserialized struct 
can easily be reused and does not contain pointers, so efficient as a 
slice (single allocation)

This allows quickly parsing everything as slices of bytes (no copy).

Versions are always *saved* sorted by modTime, newest *first*. 
No more need to sort on load.

* Allows checking if a version exists.
* Allows reading single version without unmarshal all.
* Allows reading latest version of type without unmarshal all.
* Allows reading latest version without unmarshal of all.
* Allows checking if the latest is deleteMarker by reading first entry.
* Allows adding/updating/deleting a version with only header deserialization.
* Reduces allocations on conversion to FileInfo(s).

cmd/xl-storage-format-v1.go

@@ -18,11 +18,13 @@
 package cmd
 
 import (
+	"encoding/binary"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"time"
 
+	"github.com/cespare/xxhash/v2"
 	jsoniter "github.com/json-iterator/go"
 	"github.com/minio/minio/internal/logger"
 )
@@ -205,6 +207,27 @@ func (m *xlMetaV1Object) ToFileInfo(volume, path string) (FileInfo, error) {
 	return fi, nil
 }
 
+// Signature will return a signature that is expected to be the same across all disks.
+func (m *xlMetaV1Object) Signature() [4]byte {
+	// Shallow copy
+	c := *m
+	// Zero unimportant fields
+	c.Erasure.Index = 0
+	c.Minio.Release = ""
+	crc := hashDeterministicString(c.Meta)
+	c.Meta = nil
+
+	if bts, err := c.MarshalMsg(metaDataPoolGet()); err == nil {
+		crc ^= xxhash.Sum64(bts)
+		metaDataPoolPut(bts)
+	}
+
+	// Combine upper and lower part
+	var tmp [4]byte
+	binary.LittleEndian.PutUint32(tmp[:], uint32(crc^(crc>>32)))
+	return tmp
+}
+
 // XL metadata constants.
 const (
 	// XL meta version.