Add subxt_signer crate for native & WASM compatible signing (#1016)

* Add and use subxt-signer crate for WASM compatible signing

* cargo fmt

* dev keypairs already references

* WIP fix various breakages

* re-jig features to be simpler and various test fixes etc

* doc and web fix

* fix various bits and pieces

* fix a test I broke

* dev-deps can't be linked to in docs, hrmph

* cargo fmt

* another doc link

* document the subxt_signer crate more thoroughly

* move feature flag for consistency

* more docs, no default subxt feature flag on signer, update release instrs

* Add missing license header

* unwrap_inner => into_inner

* extend a test a little to better check derive junctions

* note more clearly that the crypto bits come from sp_core::crypto

subxt/examples/tx_with_params.rs

@@ -1,6 +1,6 @@
-use sp_keyring::AccountKeyring;
 use subxt::config::polkadot::{Era, PlainTip, PolkadotExtrinsicParamsBuilder as Params};
-use subxt::{tx::PairSigner, OnlineClient, PolkadotConfig};
+use subxt::{OnlineClient, PolkadotConfig};
+use subxt_signer::sr25519::dev;
 
 #[subxt::subxt(runtime_metadata_path = "../artifacts/polkadot_metadata_small.scale")]
 pub mod polkadot {}
@@ -11,7 +11,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let api = OnlineClient::<PolkadotConfig>::new().await?;
 
     // Build a balance transfer extrinsic.
-    let dest = AccountKeyring::Bob.to_account_id().into();
+    let dest = dev::bob().public_key().into();
     let tx = polkadot::tx().balances().transfer(dest, 10_000);
 
     // Configure the transaction parameters; for Polkadot the tip and era:
@@ -20,7 +20,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .era(Era::Immortal, api.genesis_hash());
 
     // submit the transaction:
-    let from = PairSigner::new(AccountKeyring::Alice.pair());
+    let from = dev::alice();
     let hash = api.tx().sign_and_submit(&tx, &from, tx_params).await?;
     println!("Balance transfer extrinsic submitted with hash : {hash}");