migration(elections-phragmen): unreserve deposits and clear locks (#14218)

* pre_upgrade hook wip

* working pre_upgrade

* simplify code

* cleanup and document

* return reads from get_account_deposited_and_staked_sums

* improve comment

* on_runtime_upgrade comment

* post upgrade comment

* use saturating_add

* clippy

* clean up balances

* add tests

* fix comment

* oops

* actually fix comment

* fix std build

* address pr comments

* remove redundant comment

* update comment

* add comment

* oliver comments from tips pallet pr

* lint

* remove need for do_pre/do_post runtime functions

* generic dbweight

* Update frame/elections-phragmen/src/migrations/unlock_and_unreserve_all_funds.rs

Co-authored-by: Oliver Tale-Yazdi <[email protected]>

* Update frame/elections-phragmen/src/migrations/unlock_and_unreserve_all_funds.rs

Co-authored-by: Oliver Tale-Yazdi <[email protected]>

* pr comments

* remove useless check

* feature gate log target

* lint

* Update frame/elections-phragmen/src/migrations/unlock_and_unreserve_all_funds.rs

Co-authored-by: Oliver Tale-Yazdi <[email protected]>

* add log for unexpected amounts

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Co-authored-by: Oliver Tale-Yazdi <[email protected]>