Summary:
Does what it says on the can: the patch adds a hash map to `VersionStorageInfo`
that maps file numbers to file locations, i.e. (level, position in level) pairs. This
will enable stricter consistency checks in `VersionBuilder`. The patch also fixes
all the unit tests that used duplicate file numbers in a version (which would trigger
an assertion with the new code).
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6862
Test Plan:
`make check`
`make whitebox_crash_test`
Reviewed By: riversand963
Differential Revision: D21670446
Pulled By: ltamasi
fbshipit-source-id: 2eac249945cf33d8fb8597b26bfff5221e1a861a
e3f953a863