contracts: Refactor the exec module (#8604)

* contracts: Add default implementation for Executable::occupied_storage()

* contracts: Refactor the exec module

* Let runtime specify the backing type of the call stack

This removes the need for a runtime check of the specified
`MaxDepth`. We can now garantuee that we don't need to
allocate when a new call frame is pushed.

* Fix doc typo

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>

* cargo run --release --features=runtime-benchmarks --manifest-path=bin/node/cli/Cargo.toml -- benchmark --chain=dev --steps=50 --repeat=20 --pallet=pallet_contracts --extrinsic=* --execution=wasm --wasm-execution=compiled --heap-pages=4096 --output=./frame/contracts/src/weights.rs --template=./.maintain/frame-weight-template.hbs

* Review nits

* Fix defect in contract info caching behaviour

* Add more docs

* Fix wording and typos

Co-authored-by: Guillaume Thiolliere <gui.thiolliere@gmail.com>
Co-authored-by: Parity Benchmarking Bot <admin@parity.io>

substrate/frame/contracts/src/chain_extension.rs

@@ -56,7 +56,7 @@
 
 use crate::{
 	Error,
-	wasm::{Runtime, RuntimeToken},
+	wasm::{Runtime, RuntimeCosts},
 };
 use codec::Decode;
 use frame_support::weights::Weight;
@@ -171,7 +171,7 @@ where
 	///
 	/// Weight is synonymous with gas in substrate.
 	pub fn charge_weight(&mut self, amount: Weight) -> Result<()> {
-		self.inner.runtime.charge_gas(RuntimeToken::ChainExtension(amount)).map(|_| ())
+		self.inner.runtime.charge_gas(RuntimeCosts::ChainExtension(amount)).map(|_| ())
 	}
 
 	/// Grants access to the execution environment of the current contract call.
@@ -349,7 +349,7 @@ where
 			buffer,
 			allow_skip,
 			|len| {
-				weight_per_byte.map(|w| RuntimeToken::ChainExtension(w.saturating_mul(len.into())))
+				weight_per_byte.map(|w| RuntimeCosts::ChainExtension(w.saturating_mul(len.into())))
 			},
 		)
 	}