XCM revamp (#2836)

* Remove unused relaying XCM

* Aggregate HRMP (XCMP/HMP) messages. Payloads for spambot.

* Revert lock

* Fix

* Broken example

* Introduce fee payment mechanics into XCM.

* Weight limitations on XCM execution

* Mock environment for tests and the first test

* Tests for XCM and a few refactors.

* Remove code that's not ready

* Fix for an XCM and an additional test

* Query response system

* XCMP message dispatch system reimagining

- Moved most of the logic into xcm-handler pallet
- Altered the outgoing XCMP API from push to pull
- Changed underlying outgoing queue data structures to avoid multi-page read/writes
- Introduced queuing for incoming messages
- Introduced signal messages as a flow-control sub-stream
- Introduced flow-control with basic threshold back-pressure
- Introduced overall weight limitation on messages executed
- Additonal alterations to XCM APIs for the new system

* Some build fixes

* Remove the Encode bounds sprayed around

* More faff

* Fix bounds amek use latest scale codec.

* remove println

* fixes

* Fix XcmExecutor Tests

* Fix XCM bounds using derivative crate

* Refactor names of XcmGeneric &c into Xcm

* Repot the xcm-executor into xcm-builder

* Docs

* Docs

* Fixes

* Update xcm/src/lib.rs

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

* Fixes

* Docs

* Update runtime/parachains/src/ump.rs

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

* Docs

* Fixes

* Fixes

* Fixes

* Docs

* Fixes

* Fixes

* Introduce transfer_asset specialisation.

* Fixes

* Fixes

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

polkadot/Cargo.lock

@@ -160,6 +160,12 @@ version = "0.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "23b62fc65de8e4e7f52534fb52b0f3ed04746ae267519eef2a83941e8085068b"
 
+[[package]]
+name = "arrayvec"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a2f58b0bb10c380af2b26e57212856b8c9a59e0925b4c20f4a174a49734eaf7"
+
 [[package]]
 name = "asn1_der"
 version = "0.6.3"
@@ -1320,6 +1326,17 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "derivative"
+version = "2.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fcc3dd5e9e9c0b295d6e1e4d811fb6f157d5ffd784b8d202fc62eac8035a770b"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "derive_more"
 version = "0.99.11"
@@ -5054,11 +5071,11 @@ dependencies = [
 
 [[package]]
 name = "parity-scale-codec"
-version = "2.0.0"
+version = "2.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "75c823fdae1bb5ff5708ee61a62697e6296175dc671710876871c853f48592b3"
+checksum = "731f4d179ed52b1c7eeb29baf29c604ea9301b889b23ce93660220a5465d5c6f"
 dependencies = [
- "arrayvec 0.5.2",
+ "arrayvec 0.7.0",
  "bitvec",
  "byte-slice-cast",
  "parity-scale-codec-derive",
@@ -5067,9 +5084,9 @@ dependencies = [
 
 [[package]]
 name = "parity-scale-codec-derive"
-version = "2.0.0"
+version = "2.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9029e65297c7fd6d7013f0579e193ec2b34ae78eabca854c9417504ad8a2d214"
+checksum = "f44c5f94427bd0b5076e8f7e15ca3f60a4d8ac0077e4793884e6fdfd8915344e"
 dependencies = [
  "proc-macro-crate 0.1.5",
  "proc-macro2",
@@ -11307,6 +11324,7 @@ dependencies = [
 name = "xcm"
 version = "0.8.30"
 dependencies = [
+ "derivative",
  "parity-scale-codec",
 ]