Optimize listing with leaf check offloaded to posix (#7541)

Other listing optimizations include

- remove double sorting while filtering object entries
- improve error message when upload-id is not in quorum
- use jsoniter for full unmarshal json, instead of gjson
- remove unused code

cmd/storage-rest_test.go

@@ -260,7 +260,7 @@ func testStorageAPIListDir(t *testing.T, storage StorageAPI) {
 	}
 
 	for i, testCase := range testCases {
-		result, err := storage.ListDir(testCase.volumeName, testCase.prefix, -1)
+		result, err := storage.ListDir(testCase.volumeName, testCase.prefix, -1, "")
 		expectErr := (err != nil)
 
 		if expectErr != testCase.expectErr {