Allow for remapping type parameters in type substitutions (#735)

* feat!: Allow for remapping type parameters in type substitutions

* chore: cargo fmt

* chore: cargo clippy

* chore: Remove some old code

* a little tidy

* address comment nit

Co-authored-by: James Wilson <james@jsdw.me>

testing/ui-tests/src/correct/generic-params.rs

@@ -0,0 +1,67 @@
+use core::marker::PhantomData;
+
+use codec::{Decode, Encode};
+
+use subxt::utils::AccountId32;
+
+#[derive(Encode, Decode, Debug)]
+pub struct CustomAddress(u16);
+#[derive(Encode, Decode, Debug)]
+pub struct Generic<T>(T);
+#[derive(Encode, Decode, Debug)]
+pub struct Second<T, U>(U, PhantomData<T>);
+
+#[subxt::subxt(
+    runtime_metadata_path = "../../../../artifacts/polkadot_metadata.scale",
+    substitute_type(
+        type = "sp_runtime::multiaddress::MultiAddress<A, B>",
+        with = "crate::CustomAddress"
+    )
+)]
+pub mod node_runtime {}
+
+#[subxt::subxt(
+    runtime_metadata_path = "../../../../artifacts/polkadot_metadata.scale",
+    substitute_type(
+        type = "sp_runtime::multiaddress::MultiAddress<A, B>",
+        with = "crate::Generic<A>"
+    )
+)]
+pub mod node_runtime2 {}
+
+#[subxt::subxt(
+    runtime_metadata_path = "../../../../artifacts/polkadot_metadata.scale",
+    substitute_type(
+        type = "sp_runtime::multiaddress::MultiAddress<A, B>",
+        with = "crate::Generic<B>"
+    )
+)]
+pub mod node_runtime3 {}
+
+#[subxt::subxt(
+    runtime_metadata_path = "../../../../artifacts/polkadot_metadata.scale",
+    substitute_type(
+        type = "sp_runtime::multiaddress::MultiAddress<A, B>",
+        with = "crate::Second<B, A>"
+    )
+)]
+pub mod node_runtime4 {}
+
+fn main() {
+    // We assume Polkadot's config of MultiAddress<AccountId32, ()> here
+    let _ = node_runtime::tx()
+        .balances()
+        .transfer(CustomAddress(1337), 123);
+
+    let _ = node_runtime2::tx()
+        .balances()
+        .transfer(Generic(AccountId32::from([0x01;32])), 123);
+
+    let _ = node_runtime3::tx()
+        .balances()
+        .transfer(Generic(()), 123);
+
+    let _ = node_runtime4::tx()
+        .balances()
+        .transfer(Second(AccountId32::from([0x01;32]), PhantomData), 123);
+}