Generic slashing side-effects (#5623)

# Description
## What?
Make it possible for other pallets to implement their own logic when a
slash on a balance occurs.

## Why?
In the [introduction of
holds](https://github.com/paritytech/substrate/pull/12951) @gavofyork
said:
> Since Holds are designed to be infallibly slashed, this means that any
logic using a Freeze must handle the possibility of the frozen amount
being reduced, potentially to zero. A permissionless function should be
provided in order to allow bookkeeping to be updated in this instance.

At Polimec we needed to find a way to reduce the vesting schedules of
our users after a slash was made, and after talking to @Kianenigma

 at
the Web3Summit, we realized there was no easy way to implement this with
the current traits, so we came up with this solution.



## How?
- First we abstract the `done_slash` function of holds::Balanced to it's
own trait that any pallet can implement.
- Then we add a config type in pallet-balances that accepts a callback
tuple of all the pallets that implement this trait.
- Finally implement done_slash for pallet-balances such that it calls
the config type.

## Integration
The default implementation of done_slash is still an empty function, and
the new config type of pallet-balances can be set to an empty tuple, so
nothing changes by default.

## Review Notes
- I suggest to focus on the first commit which contains the main logic
changes.
- I also have a working implementation of done_slash for pallet_vesting,
should I add it to this PR?
- If I run `cargo +nightly fmt --all` then I get changes to a lot of
unrelated crates, so not sure if I should run it to avoid the fmt
failure of the CI
- Should I hunt down references to fungible/fungibles documentation and
update it accordingly?

**Polkadot address:** `15fj1UhQp8Xes7y7LSmDYTy349mXvUwrbNmLaP5tQKBxsQY1`

# Checklist

* [x] My PR includes a detailed description as outlined in the
"Description" and its two subsections above.
* [x] My PR follows the [labeling requirements](

https://github.com/paritytech/polkadot-sdk/blob/master/docs/contributor/CONTRIBUTING.md#Process
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* External contributors: ask maintainers to put the right label on your
PR.
* [ ] I have made corresponding changes to the documentation (if
applicable)

---------

Co-authored-by: Kian Paimani <[email protected]>
Co-authored-by: command-bot <>
Co-authored-by: Francisco Aguirre <[email protected]>