cumulus: add asset-hub-rococo runtime based on asset-hub-kusama and add asset-bridging support to it (#1215)

This commit adds Rococo Asset Hub dedicated runtime so we can test new
features here, before merging them in Kusama Asset Hub.
Also adds one such feature: asset transfer over bridge (Rococo AssetHub
<> Wococo AssetHub)

- clone `asset-hub-kusama-runtime` -> `asset-hub-rococo-runtime`
- make it use Rococo primitives, names, assets, constants, etc
- add asset-transfer-over-bridge support to Rococo AssetHub <> Wococo
AssetHub

Fixes #1128

---------

Co-authored-by: Branislav Kontur <bkontur@gmail.com>
Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>

cumulus/parachains/runtimes/assets/asset-hub-rococo/build.rs

@@ -0,0 +1,26 @@
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#[cfg(feature = "std")]
+fn main() {
+	substrate_wasm_builder::WasmBuilder::new()
+		.with_current_project()
+		.export_heap_base()
+		.import_memory()
+		.build()
+}
+
+#[cfg(not(feature = "std"))]
+fn main() {}