Allow transaction for offchain indexing (#7290)

* Moving offchain change set to state machine overlay change set,
preparing use of change set internally.

* Make change set generic over key and value, and use it for offchain
indexing.

* test ui change

* remaining delta

* generating with standard method

* Remove 'drain_committed' function, and documentation.

* Default constructor for enabling offchain indexing.

* Remove offchain change specific iterators.

* remove pub accessor

* keep previous hierarchy, just expose iterator instead.

* Update primitives/state-machine/src/overlayed_changes/mod.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* fix line break

* missing renamings

* fix import

* fix new state-machine tests.

* Don't expose InnerValue type.

* Add test similar to set_storage.

* Remove conditional offchain storage (hard to instantiate correctly).

* fix

* offchain as children cannot fail if top doesn't

Co-authored-by: Addie Wagenknecht <addie@nortd.com>
Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

substrate/client/api/src/backend.rs

@@ -21,12 +21,12 @@
 use std::sync::Arc;
 use std::collections::{HashMap, HashSet};
 use sp_core::ChangesTrieConfigurationRange;
-use sp_core::offchain::{OffchainStorage,storage::OffchainOverlayedChanges};
+use sp_core::offchain::OffchainStorage;
 use sp_runtime::{generic::BlockId, Justification, Storage};
 use sp_runtime::traits::{Block as BlockT, NumberFor, HashFor};
 use sp_state_machine::{
 	ChangesTrieState, ChangesTrieStorage as StateChangesTrieStorage, ChangesTrieTransaction,
-	StorageCollection, ChildStorageCollection,
+	StorageCollection, ChildStorageCollection, OffchainChangesCollection,
 };
 use sp_storage::{StorageData, StorageKey, PrefixedStorageKey, ChildInfo};
 use crate::{
@@ -174,7 +174,7 @@ pub trait BlockImportOperation<Block: BlockT> {
 	/// Write offchain storage changes to the database.
 	fn update_offchain_storage(
 		&mut self,
-		_offchain_update: OffchainOverlayedChanges,
+		_offchain_update: OffchainChangesCollection,
 	) -> sp_blockchain::Result<()> {
 		 Ok(())
 	}