This PR:
- moves `validate_xcm_nesting` from `XcmpQueue` into the `VersionedXcm`
- adds `validate_xcm_nesting` to the `ParentAsUmp`
- adds `validate_xcm_nesting` to the `ChildParachainRouter`


Based on discussion
[here](https://github.com/paritytech/polkadot-sdk/pull/4186#discussion_r1571344270)
and/or
[here](https://github.com/paritytech/polkadot-sdk/pull/4186#discussion_r1572076666)
and/or [here]()

## Question/TODO

- [x] To the
[comment](https://github.com/paritytech/polkadot-sdk/pull/4186#discussion_r1572072295)
- Why was `validate_xcm_nesting` added just to the `XcmpQueue` router
and nowhere else? What kind of problem `MAX_XCM_DECODE_DEPTH` is
solving? (see
[comment](https://github.com/paritytech/polkadot-sdk/pull/4236#discussion_r1574605191))