Support constructing and submitting V5 transactions (#1931)

* TransactionExtensions basic support for V5 VerifySignature and renames

* WIP: subxt-core v5 transaction support

* Subxt to support V5 extrinsics

* WIP tests failing with wsm trap error

* Actually encode mortality to fix tx encode issue

* fmt

* rename to sign_with_account_and_signature

* Add explicit methods for v4 and v5 ext construction

* clippy

* fix wasm example and no mut self where not needed

* fix doc example

* another doc fix

* Add tests for tx encoding and fix v5 encode issue

* add copyright and todo

* refactor APIs to have clear v4/v5 split in core and slightly nicer split in subxt proper

* rename Partial/SubmittableExtrinsic to *Transaction

* Remove SignerT::address since it's not needed

* doc fixes

* fmt

* doc fixes

* Fix comment number

* Clarify panic behaviour of inject_signature

* fmt

subxt/examples/rpc_legacy.rs

@@ -38,12 +38,8 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         let current_nonce = rpc
             .system_account_next_index(&alice.public_key().into())
             .await?;
-        let current_header = rpc.chain_get_header(None).await?.unwrap();
 
-        let ext_params = Params::new()
-            .mortal(&current_header, 8)
-            .nonce(current_nonce)
-            .build();
+        let ext_params = Params::new().mortal(8).nonce(current_nonce).build();
 
         let balance_transfer = polkadot::tx()
             .balances()
@@ -51,7 +47,8 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
         let ext_hash = api
             .tx()
-            .create_signed_offline(&balance_transfer, &alice, ext_params)?
+            .create_partial_offline(&balance_transfer, ext_params)?
+            .sign(&alice)
             .submit()
             .await?;