Refactor transaction message implementation

[RongtongJin]

FEATURE REQUEST

1. Please describe the feature you are requesting.

The current implementation of rocketmq transaction message is not elegant. So I want to refactor the implementation of transaction message.

2. Provide any additional detail on your proposed use case for this feature.

3. Indicate the importance of this issue to you (blocker, must-have, should-have, nice-to-have). Are you currently using any workarounds to address this issue?