feature(Tianmu): Refactor the Tianmu storage engine.

[RingsC]

Is your feature request related to a problem? Please describe.

Due to the chaotic logic of Tianmu engine. Such as call-relationship, the non-clear relationship between rcbase_hton, ha_rcengine_ and ha_kvstore_.

Especially in sql\sql_optimizer.cc, JOIN::optimize introudces a variable part to describe the which part we are in. That's a ugly code.

the fiiles are following:

storage/tianmu/handler/tianmu_handler_com.cpp
sql\sql_parser.cc

Describe the solution you'd like

Making the clean code. the relationships in Tiamu will be in a clean status, just as InnoDB does.

Describe alternatives you've considered

Additional context