Add tool to read on-chain storage

[montyly]

We can rely on the internal storage information and web3.get_storage_at to return the value of a contract onchain

Example of API

• slither-read-storage [codebase] 0x414141 canonical_variable_name
• slither-read-storage 0x414141 canonical_variable_name (if the source code is on etherscan)

Potential flags:

• RPC-related to connect to local node, infrura or other
• --list-all to dump all the contract variables and their values (aside mapping and maybe array?)
• --offset / --index for mapping array

[Elyx0]

Came from https://0xalpharush.github.io/slithering-through-the-dark-forest/ excited to see it!

[jeffchen006]

Redirect interested people to https://github.com/crytic/slither/tree/master/slither/tools/read_storage