Calculate and refund weight for identity pallet (#5680)

* add old_registrar_count as param to estimate weight

* cast count to Weight

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* add weight calculation for set_identity

* remove superfluous weight comment

* add detailed weight estimation for set_subs

* adjust benchmarking code to the new API

* add second parameter to set_subs benchmark

* rename o to p

* calculate weight based on benchmarks

* use try_mutate for registrars

* fix weight number typo

* update weights for set_subs + add weights for clear_identity and request_judgement

* improve naming and docs

* add weight calculation for cancel_request

* fix benchmark

* fix tests

* fix arithmetic overflow in balances triggered by tests

* add weight calcluations for more dispatchables

* add weight calculation for provide_judgement

* mark param as unused

* add MaxRegistrars associated type used for weight estimation

* check that MaxRegistrars is not exceeded

* add remaining weight calculations

* use weight refunds to use more constants in weight estimation

* adjust usage of clear_identity

* refund request_judgement weights and remove param

* refund weights for cancel_request and remove param

* add remaining refunds and remove params

* refund weight for set_subs and remove param

* make comment more specific

* add range note to benchmarking docs

* fix inconsistencies before review

* fix actual weight calculation for add_registrar

* remove duplicate balance ops weights + refund on all dispatchables

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>