Paddlebox-add merge func

[goodcoder-cnn]

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[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
2 out of 5 committers have signed the CLA.

:white_check_mark: hutuxian
:white_check_mark: ForFishes
:x: daianyu
:x: qingshui
:x: inoration

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[paddle-bot-old[bot]]

Thanks for your contribution! Please wait for the result of CI firstly. See Paddle CI Manual for details.

[paddle-bot-old[bot]]

❌This PR is not created using PR's template. You can refer to this Demo. Please use PR's template, it helps save our maintainers' time so that more developers get helped.

[paddle-bot[bot]]

很抱歉，经过我们的反复讨论，你的PR暂未达到合入标准，请阅读飞桨原生算子开发规范，你可以重新提交新的PR，我们先将此PR关闭，感谢你的贡献。 Sorry to inform you that through our discussion, your PR fails to meet the merging standard (Reference: Paddle Custom Operator Design Doc). You can also submit an new one. Thank you.