refactor(split): move replica split functions into replica_split_manager class

[hycdong]

In previous implmentation, split varieties and functions are defined in replica.h, this pull request adds a new class replica_split_manager and moves them into this class.

• move split varieties and functions definition from replica.h to split/replica_split_manager.h
• move split function implementation from replica_split.cpp to split/replica_split_manager.cpp
• move split unit test from test/replica_split_test.cpp into split/test/replica_split_test.cpp

By the way, code of split will be deep refactored in further pull request, this pull request only does basic refactor to add replica_split_manager class.

[neverchanje]

move split varieties and functions definition from replica.h to partition_split/replica_split_manager.h

Name the directory to split. "partition_split" is too long.

[hycdong]

move split varieties and functions definition from replica.h to partition_split/replica_split_manager.h

Name the directory to split. "partition_split" is too long.

Done

[levy5307]

why didn't you name it partition_split_manager?

[hycdong]

The class name is replica_split_manager, showing the function is partition_split, and it is used for replica, just like replica_bulk_loader.

[levy5307]

But I saw some comments write Partition Split, this will make someone new confused with it.

[hycdong]

The suitable class name may be replica_partition_split_manager, but it is a little long, so I name it replica_split_manager, split is the abbreviation of partition split. Could you please tell me what is your confusion raised by partition split?

[levy5307]

I think it is better to give it a uniform name. or someone without a relevant knowledge background may feel confused with what's the difference between partition split and replica split

[neverchanje]

Partition Split is the user-facing word. Inside the implementation, child/parent replica both do the split job, in replica level. So replica_split_manager is more accurate.

Futhermore, it would be better if child and parent could be separated to different classes.