title: Prevents staking controllers from becoming stashes of different ledgers; Ensures that no ledger in bad state is mutated.

doc:
  - audience: Runtime User
    description: |
      This PR introduces a fix to the staking logic which prevents an existing controller from bonding as a stash of another ledger, which
      lead to staking ledger inconsistencies down the line. In addition, it adds a few (temporary) gates to prevent ledgers that are already
      in a bad state from mutating its state.

      In summary:
      * Checks if stash is already a controller when calling `Call::bond` and fails if that's the case;
      * Ensures that all fetching ledgers from storage are done through the `StakingLedger` API;
      * Ensures that a `Error::BadState` is returned if the ledger bonding is in a bad state. This prevents bad ledgers from mutating (e.g.
        `bond_extra`, `set_controller`, etc) its state and avoid further data inconsistencies.
      * Prevents stashes which are controllers or another ledger from calling `set_controller`, since that may lead to a bad state.
      * Adds further try-state runtime checks that check if there are ledgers in a bad state based on their bonded metadata.

crates:
- name: pallet-staking