Metadata V16: Be more dynamic over which hasher is used. (#1974)

* Use DynamicHasher256 to support Blake2 or Keccack depending on chain

* remove Config::Hash associated type, replace with HashFor<Config> alias

* Fix doc links

* fix wasm tests

* Don't strip system pallet associated types. check System.Hashing, not Hash. Rename BlockHash trait to Hash

* Tweak comment

* fmt

* fix merge

* Fix typo

testing/integration-tests/src/full_client/frame/contracts.rs

@@ -12,7 +12,12 @@ use crate::{
     subxt_test, test_context, TestClient, TestConfig, TestContext,
 };
 use subxt::ext::futures::StreamExt;
-use subxt::{tx::TxProgress, utils::MultiAddress, Config, Error};
+use subxt::{
+    config::{Config, HashFor},
+    tx::TxProgress,
+    utils::MultiAddress,
+    Error,
+};
 use subxt_signer::sr25519::{self, dev};
 
 struct ContractsTestContext {
@@ -20,7 +25,7 @@ struct ContractsTestContext {
     signer: sr25519::Keypair,
 }
 
-type Hash = <TestConfig as Config>::Hash;
+type Hash = HashFor<TestConfig>;
 type AccountId = <TestConfig as Config>::AccountId;
 
 /// A dummy contract which does nothing at all.