Use scale-encode and scale-decode to encode and decode based on metadata (#842)

* WIP EncodeAsType and DecodeAsType

* remove silly cli experiment code

* Get things finally compiling with EncodeAsType and DecodeAsType

* update codegen test and WrapperKeepOpaque proper impl (in case it shows up in codegen)

* fix tests

* accomodate scale-value changes

* starting to migrate to EncodeAsType/DecodeAsType

* static event decoding and tx encoding to use DecodeAsFields/EncodeAsFields

* some tidy up and add decode(skip) attrs where needed

* fix root event decoding

* #[codec(skip)] will do, and combine map_key stuff into storage_address since it's all specific to that

* fmt and clippy

* update Cargo.lock

* remove patched scale-encode

* bump scale-encode to 0.1 and remove unused dep in testing crate

* update deps and use released scale-decode

* update scale-value to latest to remove git branch

* Apply suggestions from code review

Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>

* remove sorting in derives/attr generation; spit them out in order given

* re-add derive sorting; it's a hashmap

* StaticTxPayload and DynamicTxPayload rolled into single Payload struct

* StaticStorageAddress and DynamicStorageAddress into single Address struct

* Fix storage address byte retrieval

* StaticConstantAddress and DynamicConstantAddress => Address

* Simplify storage codegen to fix test

* Add comments

* Alias to RuntimeEvent rather than making another, and prep for substituting call type

* remove unnecessary clone

* Fix docs and failing UI test

* root_bytes -> to_root_bytes

* document error case in StorageClient::address_bytes()

---------

Co-authored-by: Alexandru Vasile <60601340+lexnv@users.noreply.github.com>

examples/examples/storage_iterating.rs

@@ -10,12 +10,11 @@
 //! polkadot --dev --tmp
 //! ```
 
-use codec::Decode;
+use codec::{
+    Decode,
+    Encode,
+};
 use subxt::{
-    storage::address::{
-        StorageHasher,
-        StorageMapKey,
-    },
     OnlineClient,
     PolkadotConfig,
 };
@@ -83,11 +82,13 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         let mut query_key = key_addr.to_root_bytes();
 
         // We know that the first key is a u32 (the `XcmVersion`) and is hashed by twox64_concat.
-        // We can build a `StorageMapKey` that replicates that, and append those bytes to the above.
-        StorageMapKey::new(2u32, StorageHasher::Twox64Concat).to_bytes(&mut query_key);
+        // twox64_concat is just the result of running the twox_64 hasher on some value and concatenating
+        // the value itself after it:
+        query_key.extend(subxt::ext::sp_core::twox_64(&2u32.encode()));
+        query_key.extend(&2u32.encode());
 
         // The final query key is essentially the result of:
-        // `twox_128("XcmPallet") ++ twox_128("VersionNotifiers") ++ twox_64(2u32) ++ 2u32`
+        // `twox_128("XcmPallet") ++ twox_128("VersionNotifiers") ++ twox_64(scale_encode(2u32)) ++ scale_encode(2u32)`
         println!("\nExample 3\nQuery key: 0x{}", hex::encode(&query_key));
 
         let keys = api