Refactors staking and stake-tracker so that target and voter lists include idle stakers

[gpestana]

In this PR we change the current assumptions so that TargetList and VoterList also keep track of the idle stakers (w.g. chilled) and the target scores are tracked and updated even while the validator is chilled. The idle stakers will be removed when the ledger unbonds.

This allows the stake-tracker to keep track of the chilled validators and respective score so that a re-validate of a chilled validator is brought up with the correct target score (i.e. self stake + all current nominations in the system).

[gpestana]

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@gpestana Command "$PIPELINE_SCRIPTS_DIR/commands/fmt/fmt.sh" has finished. Result: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4490137 has finished. If any artifacts were generated, you can download them from https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4490137/artifacts/download.