cli: consolidate `erigon seg clearIndexing` into `erigon seg accessor --rebuild`

- `clearIndexing` does gen new salt.txt. `erigon seg accessor --rebuild` doesn't. need add flag `--new-salt` which will support it
- ensure `erigon seg accessor --rebuild` does rebuild and block accessors and state accessors. add unit-test for it.

Dictionary:
- `accessors` - `.idx, .efi, .vi, .bt` files. usually not exposed by API for high-level code or user. technical detail of implementation (how do we store data on disk).
- `index` (or `inverted_index`) - high-level user-facing concept, with public API. Technically can be implemented as many various files on disk (segments + accessors).