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/Cargo.toml

@@ -25,6 +25,7 @@ assert_matches = "1.1"
 hex-literal = "0.2.0"
 consensus = { package = "srml-consensus", path = "../consensus" }
 balances = { package = "srml-balances", path = "../balances" }
+hex = "0.3"
 
 [features]
 default = ["std"]