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/substrate_compat_signer.rs

@@ -69,10 +69,6 @@ mod pair_signer {
             self.account_id.clone()
         }
 
-        fn address(&self) -> <PolkadotConfig as Config>::Address {
-            self.account_id.clone().into()
-        }
-
         fn sign(&self, signer_payload: &[u8]) -> <PolkadotConfig as Config>::Signature {
             let signature = self.signer.sign(signer_payload);
             MultiSignature::Sr25519(signature.0)