Migrate pallet-session and session-historical to pallet attribute macro

[stanly-johnson]

Part of #7882.

Converts the session and session-historical pallet to the new pallet attribute macro introduced in #6877.

Following the upgrade guidelines here: https://crates.parity.io/frame_support/attr.pallet.html#upgrade-guidelines.

⚠️ Breaking Change ⚠️

From https://crates.parity.io/frame_support/attr.pallet.html#checking-upgrade-guidelines

storages now use PalletInfo for module_prefix instead of the one given to decl_storage: Thus any use of this pallet in construct_runtime! should be careful to update name in order not to break storage or to upgrade storage (moreover for instantiable pallet). If pallet is published, make sure to warn about this breaking change.

[KiChjang]

@stanly-johnson Please use tabs in the modified files per our coding standards. Thanks!

[KiChjang]

Migration looks good, but I can still see spaces with some of these files.

[KiChjang]

CI is spitting out errors:

error: use of deprecated type alias `pallet_session::Module`: use `Pallet` instead
   --> frame/staking/src/lib.rs:657:4
    |
657 |         <pallet_session::Module<T>>::disable(validator)
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `-D deprecated` implied by `-D warnings`
error: use of deprecated type alias `pallet_session::Module`: use `Pallet` instead
   --> frame/staking/src/lib.rs:661:4
    |
661 |         <pallet_session::Module<T>>::validators()
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^
error: use of deprecated type alias `pallet_session::historical::Module`: use `Pallet` instead
   --> frame/staking/src/lib.rs:665:4
    |
665 |         <pallet_session::historical::Module<T>>::prune_up_to(up_to);
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 3 previous errors

[shawntabrizi]

This is a breaking change. The historical pallet will no longer use the Session storage.

This needs a storage migration.

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[shawntabrizi]

Still needs a storage migration

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.