Migrate Pallets to Named Events

[shawntabrizi]

The #[pallet::event] macro supports named structs for events, which provides better UX to users listening and accessing events.

To migrate the events you need to:

1. Search for #[pallet::event] enum definitions
2. Switch events from unnamed tuples to named structs
3. Clean up comments which manually labeled the unnamed tuple elements
4. Fix all usage of the new struct
5. Format, compile, and run tests using features=runtime-benchmarks

Should be non-breaking and backwards compatible.

See an example: #5423

[shawntabrizi]

still more to do here :)