KVCache use MinBlocksInfo to get start/count in query

[Change72]

Use MinBlocksInfo to get start/count in the query (touched blocks). The start/count will be saved in KVCache and will be used in partial overlap cases in the future.

In the current code, MinBlocksInfoMap will temporarily hold the minBlocksInfo in memory in order to avoid the repeat MinBlocksInfo(*VB, Req.RelStep); for the same variable.

However, MinBlocksInfoMap only works for mode::deferred, and not for mode::Sync.

[pnorbert]

Just move MinBlocksInfoMap to be a private class member, and free it up in EndStep(). Then it should work with Sync mode as well.