Store validator self-vote in bags-list, and allow them to be trimmed for election (#10821)

* Implement the new validator-in-bags-list scenario + migration

* Apply suggestions from code review

Co-authored-by: Zeke Mostov <[email protected]>

* some review comments

* guard the migration

* some review comments

* Fix tests 🤦

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* Fix build

* fix weight_of_fn

* reformat line width

* make const

* use weight of fn cached

* SortedListProvider -> VoterList

* Fix all build and docs

* check post migration

Co-authored-by: Zeke Mostov <[email protected]>