Make offchain indexing work (#7940)

* Make offchain indexing work

This fixes some bugs with offchain indexing to make it actually working ;)

* Fix tests

* Fix browser build

* Update client/db/src/offchain.rs

Co-authored-by: cheme <emericchevalier.pro@gmail.com>

* Remove seperation between prefix and key

Co-authored-by: cheme <emericchevalier.pro@gmail.com>

substrate/Cargo.lock

@@ -7218,12 +7218,14 @@ dependencies = [
  "parity-scale-codec",
  "parking_lot 0.11.1",
  "rand 0.7.3",
+ "sc-block-builder",
  "sc-client-api",
  "sc-client-db",
  "sc-keystore",
  "sc-network",
  "sc-transaction-pool",
  "sp-api",
+ "sp-consensus",
  "sp-core",
  "sp-offchain",
  "sp-runtime",