More tests and checks confirming that `ledger.controller` is always correct. (#2599)

A bonded ledger fetched with the `StakingLedger` implementation exposes
a method `ledger.controller()` that returns the controller of the
ledger. However, that controller is computed and stored under the
`ledger.controller` field on the fly - i.e when the ledger is fetched
from storage using the `StakingLedger::get` method. The controller field
is never stored in storage.

This PR add a few more tests checks and improves the ledger try-state
checks to make sure these invariants hold true.

---------

Co-authored-by: command-bot <>
Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: Kian Paimani <[email protected]>