CheckWeight: account for extrinsic len as proof size (#4765)

Fix https://github.com/paritytech/polkadot-sdk/issues/4743 which allows
us to remove the defensive limit on pov size in Cumulus after relay
chain gets upgraded with these changes. Also add unit test to ensure
`CheckWeight` - `StorageWeightReclaim` integration works.

TODO:
- [x] PRDoc
- [x] Add a len to all the other tests in storage weight reclaim and
call `CheckWeight::pre_dispatch`

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Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>