PoV Reclaim (Clawback) Node Side (#1462)

This PR provides the infrastructure for the pov-reclaim mechanism
discussed in #209. The goal is to provide the current proof size to the
runtime so it can be used to reclaim storage weight.

## New Host Function
- A new host function is provided
[here](https://github.com/skunert/polkadot-sdk/blob/5b317fda3be205f4136f10d4490387ccd4f9765d/cumulus/primitives/pov-reclaim/src/lib.rs#L23).
It returns the size of the current proof size to the runtime. If
recording is not enabled, it returns 0.

## Implementation Overview
- Implement option to enable proof recording during import in the
client. This is currently enabled for `polkadot-parachain`,
`parachain-template` and the cumulus test node.
- Make the proof recorder ready for no-std. It was previously only
enabled for std environments, but we need to record the proof size in
`validate_block` too.
- Provide a recorder implementation that only the records the size of
incoming nodes and does not store the nodes itself.
- Fix benchmarks that were broken by async backing changes
- Provide new externalities extension that is registered by default if
proof recording is enabled.
- I think we should discuss the naming, pov-reclaim was more intuitive
to me, but we could also go with clawback like in the issue.

## Impact of proof recording during import
With proof recording: 6.3058 Kelem/s
Without proof recording: 6.3427 Kelem/s

The measured impact on the importing performance is quite low on my
machine using the block import benchmark. With proof recording I am
seeing a performance hit of 0.585%.

---------

Co-authored-by: command-bot <>
Co-authored-by: Davide Galassi <davxy@datawok.net>
Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/primitives/trie/Cargo.toml

@@ -34,6 +34,7 @@ trie-db = { version = "0.28.0", default-features = false }
 trie-root = { version = "0.18.0", default-features = false }
 sp-core = { path = "../core", default-features = false}
 sp-std = { path = "../std", default-features = false}
+sp-externalities = { path = "../externalities", default-features = false }
 schnellru = { version = "0.2.1", optional = true }
 
 [dev-dependencies]
@@ -58,6 +59,7 @@ std = [
 	"scale-info/std",
 	"schnellru",
 	"sp-core/std",
+	"sp-externalities/std",
 	"sp-runtime/std",
 	"sp-std/std",
 	"thiserror",