Contract restoration (#2502)

* partial impl

* more checks

* improve TestExternalities + tests

* make tombstone raw to derive Eq

* remove before merge

* add test

* fmt

* update test

* doc

* bump version

* fix testing

* update runtime

* Fix TrieIdGenerator

* fix dummy trie id generator

* update test

* bump version

* format

* Update core/state-machine/src/testing.rs

Co-Authored-By: cheme <emericchevalier.pro@gmail.com>

* document test

* Apply suggestions from code review

Co-Authored-By: DemiMarie-temp <50585338+DemiMarie-temp@users.noreply.github.com>

* refactor

* fix

* fmt

* address review

* impl last_write

* Fix storage size, test, remove size in tombstone

* fix

* Update srml/contract/src/lib.rs

Co-Authored-By: Sergei Pepyakin <s.pepyakin@gmail.com>

* comment

* child_storage_root as &[u8]

substrate/srml/contract/src/rent.rs

@@ -163,9 +163,8 @@ fn try_evict_or_and_pay_rent<T: Trait>(
 			// Note: this operation is heavy.
 			let child_storage_root = runtime_io::child_storage_root(&contract.trie_id);
 
-			let tombstone = TombstoneContractInfo::new(
-				child_storage_root,
-				contract.storage_size,
+			let tombstone = <TombstoneContractInfo<T>>::new(
+				&child_storage_root[..],
 				contract.code_hash,
 			);
 			<ContractInfoOf<T>>::insert(account, ContractInfo::Tombstone(tombstone));