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/Cargo.lock

@@ -4799,6 +4799,7 @@ dependencies = [
  "rand 0.8.3",
  "rand_pcg 0.3.0",
  "serde",
+ "smallvec 1.6.1",
  "sp-core",
  "sp-io",
  "sp-runtime",