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/executive/src/lib.rs

@@ -474,7 +474,7 @@ mod tests {
 				header: Header {
 					parent_hash: [69u8; 32].into(),
 					number: 1,
-					state_root: hex!("ac2840371d51ff2e036c8fc05af7313b7a030f735c38b2f03b94cbe87bfbb7c9").into(),
+					state_root: hex!("5ba497e45e379d80a4524f9509d224e9c175d0fa30f3491481e7e44a6a758adf").into(),
 					extrinsics_root: hex!("03170a2e7597b7b7e3d84c05391d139a62b157e78786d8c082f29dcf4c111314").into(),
 					digest: Digest { logs: vec![], },
 				},