revamp locking & reserving

[sam0x17]

Description

This PR is our initial stab at #12918, which involves revisiting the definitions of free, locked, and reserved, especially as these concepts relate to voting, aucitions/crowdloans, and staking. In particular reserving will be replaced with "holding" via a type-safe HoldReason, and

This will entail:

• [ ] generic #[pallet::composite] syntax for definining composite enums that can then be used at the runtime level
• [ ] HoldReason / type-safe reserve/hold identifier via #[pallet::composite]
• [ ] FreezeReason / type-safe lock/freeze identifier via #[pallet::composite]
• [ ] TBD, see original issue #12918

Related Issued

• #12918