Avoid using jsoniter, move to fastjson (#8063)

This is to avoid using unsafe.Pointer type
code dependency for MinIO, this causes
crashes on ARM64 platforms

Refer #8005 collection of runtime crashes due
to unsafe.Pointer usage incorrectly. We have
seen issues like this before when using
jsoniter library in the past.

This PR hopes to fix this using fastjson

cmd/fs-v1.go

@@ -38,6 +38,7 @@ import (
 	"github.com/minio/minio/pkg/mimedb"
 	"github.com/minio/minio/pkg/mountinfo"
 	"github.com/minio/minio/pkg/policy"
+	"github.com/valyala/fastjson"
 )
 
 // Default etag is used for pre-existing objects.
@@ -1092,13 +1093,22 @@ func (fs *FSObjects) getObjectETag(ctx context.Context, bucket, entry string, lo
 		return "", toObjectErr(err, bucket, entry)
 	}
 
+	parser := fsParserPool.Get()
+	defer fsParserPool.Put(parser)
+
+	var v *fastjson.Value
+	v, err = parser.ParseBytes(fsMetaBuf)
+	if err != nil {
+		return "", toObjectErr(err, bucket, entry)
+	}
+
 	// Check if FS metadata is valid, if not return error.
-	if !isFSMetaValid(parseFSVersion(fsMetaBuf)) {
+	if !isFSMetaValid(parseFSVersion(v)) {
 		logger.LogIf(ctx, errCorruptedFormat)
 		return "", toObjectErr(errCorruptedFormat, bucket, entry)
 	}
 
-	return extractETag(parseFSMetaMap(fsMetaBuf)), nil
+	return extractETag(parseFSMetaMap(v)), nil
 }
 
 // ListObjects - list all objects at prefix upto maxKeys., optionally delimited by '/'. Maintains the list pool