[improve] extract field in value that already contains in key

[leaves12138]

The key-value storage (in primary-key table) are redundant. Now, the format of a row is: _KEY_a, _KEY_b, _FIELD_SEQUENCE, _ROW_KIND, a, b, c, d, e, f, g The column "a" and "b" have double restored. A optimization is:

convert    _KEY_a, _KEY_b, _FIELD_SEQUENCE, _ROW_KIND, a, b, c, d, e, f, g

to         _KEY_a, _KEY_b, _FIELD_SEQUENCE, _ROW_KIND, c, d, e, f, g

While reading, we find the a, b from key and fill them to value.

This PR is not complete, unit tests and compatibility test will need to be done.