We create a new segment format for BetaRowset. New format merge
data file and index file into one file. And we create a new format
for short key index. In origin code index is stored in format like
RowCusor which is not efficient to compare. Now we encode multiple
column into binary, and we assure that this binary is sorted same
with the key columns.
NOTE: This patch would modify all Backend's data.
And this will cause a very long time to restart be.
So if you want to interferer your product environment,
you should upgrade backend one by one.
1. Refactoring be is to clarify the structure the codes.
2. Use unique id to indicate a rowset.
Nameing rowset with tablet_id and version will lead to
many conflicts among compaction, clone, restore.
3. Extract an rowset interface to encapsulate rowsets
with different format.
