ExtrinsicV5: Add new General() creation option

[haerdib]

For offline Extrinsic composition, we currently offer the "bare" version (previously unsigned) and the "Signed" one. With V5 there's now a third option called "General":

https://github.com/paritytech/polkadot-sdk/blob/350a6c4ccc4c2f376b9f5ed259daf3a56d5fed56/substrate/primitives/runtime/src/generic/unchecked_extrinsic.rs#L73-L91

We should match this possibility in our compose functions.

[haerdib]

With V5 and the Extrinsic Horizon, the extrinisc params get a much more important standing and probably need to be adapted a lot mroe than they have been. More infos here:

• https://forum.polkadot.network/t/introducing-transactionextension/10827
• Extrinsic Horizon paritytech/polkadot-sdk#2415
• Example pallet with mock and tests: https://github.com/paritytech/polkadot-sdk/tree/master/substrate/frame/examples/authorization-tx-extension/src

So far, I think our extrinsic_params handling very complicated and not user-friendly. I therefore propose a breaking change.

Current situation: "manual" definition of GenericTxExtension and GenericImplicit that need to match in their order and the users need to know which type is used when (e.g. checking each extension separately):

substrate-api-client/primitives/src/extrinsics/extrinsic_params.rs

Lines 28 to 45 in 1f040e0

	/// TxExtension that is compatible with a default Substrate / Polkadot node.
	// Unlike the TxExtension on the node side, which seemingly contains a lot more parameters
	// see: https://github.com/paritytech/polkadot-sdk/blob/c139739868eddbda495d642219a57602f63c18f5/substrate/bin/node/runtime/src/lib.rs#L2665-L2678
	// The TxExtension on the client side mirrors the actual values contained. E.g.
	// CheckNonZeroSender does not hold any value inside (see link below)
	// https://github.com/paritytech/polkadot-sdk/blob/c139739868eddbda495d642219a57602f63c18f5/substrate/frame/system/src/extensions/check_non_zero_sender.rs#L32
	// and is therefore not represented on this side of the TxExtension.
	// The Era however is actually defined in the CheckMortality part:
	// https://github.com/paritytech/polkadot-sdk/blob/c139739868eddbda495d642219a57602f63c18f5/substrate/frame/system/src/extensions/check_mortality.rs#L39
	// and needs to be defined here. Be sure the order matches the one on the node side.
	#[derive(Decode, Encode, Copy, Clone, Eq, PartialEq, Debug, TypeInfo)]
	pub struct GenericTxExtension<Tip, Index> {
	pub era: Era,
	#[codec(compact)]
	pub nonce: Index,
	pub tip: Tip,
	pub check_hash: u8,
	}

substrate-api-client/primitives/src/extrinsics/extrinsic_params.rs

Lines 71 to 81 in 1f040e0

	/// Default implicit fields of a Polkadot/Substrate node.
	// Order: (CheckNonZeroSender, CheckSpecVersion, CheckTxVersion, CheckGenesis, CheckEra, CheckNonce, CheckWeight,
	// transactionPayment::ChargeTransactionPayment, CheckMetadataHash, WeightReclaim).
	// The order and types must match the one defined in the runtime.
	// Example: https://github.com/paritytech/polkadot-sdk/blob/c139739868eddbda495d642219a57602f63c18f5/substrate/bin/node/runtime/src/lib.rs#L2665-L2678
	// The `Implicit` is the tuple returned from the call TransactionExtension::implicit().
	// Each member defined in the `TxExtension` on the node side implements the trait `TransactionExtension`, which
	// defines what is returned upon the `implicit` call. The Implicit defined here
	// must mirror these return values.
	// Example: https://github.com/paritytech/polkadot-sdk/blob/c139739868eddbda495d642219a57602f63c18f5/substrate/frame/system/src/extensions/check_mortality.rs#L62
	pub type GenericImplicit<Hash> = ((), u32, u32, Hash, Hash, (), (), (), Option<H256>, ());

Proposed change:
Implement a simplified mirror of popular extensions. They themselves know their implicit, resp. their TxExtension output. The user only needs to specify the order once, simply matching the one specified in the runtime.

I will make a test PR showing how that could look like.