Fixes#2892
IMPORTANT NOTICE: this CL makes incompatible changes to V2 storage format, developers need to create new tables for test.
This CL refactors the metadata and page format for segment_v2 in order to
* make it easy to extend existing page type
* make it easy to add new page type while not sacrificing code reuse
* make it possible to use SIMD to speed up page decoding
Here we summary the main code changes
* Page and index metadata is redesigned, please see `segment_v2.proto`
* The new class `PageIO` is the single place for reading and writing all pages. This removes lots of duplicated code. `PageCompressor` and `PageDecompressor` are now useless and removed.
* The type of value ordinal is changed from `rowid_t` to 64-bits `ordinal_t`, this affects ordinal index as well.
* Column's ordinal index is now implemented by IndexPage, the same with IndexedColumn.
* Zone map index is now implemented by IndexedColumn
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