[Bridges] Move chain definitions to separate folder (#3822)

Related to
https://github.com/paritytech/parity-bridges-common/issues/2538

This PR doesn't contain any functional changes. 

The PR moves specific bridged chain definitions from
`bridges/primitives` to `bridges/chains` folder in order to facilitate
the migration of the `parity-bridges-repo` into `polkadot-sdk` as
discussed in https://hackmd.io/LprWjZ0bQXKpFeveYHIRXw?view

Apart from this it also includes some cosmetic changes to some
`Cargo.toml` files as a result of running `diener workspacify`.

bridges/chains/chain-asset-hub-rococo/Cargo.toml

@@ -0,0 +1,29 @@
+[package]
+name = "bp-asset-hub-rococo"
+description = "Primitives of AssetHubRococo parachain runtime."
+version = "0.4.0"
+authors.workspace = true
+edition.workspace = true
+license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
+
+[lints]
+workspace = true
+
+[dependencies]
+codec = { package = "parity-scale-codec", version = "3.1.5", default-features = false }
+scale-info = { version = "2.10.0", default-features = false, features = ["derive"] }
+
+# Substrate Dependencies
+frame-support = { path = "../../../substrate/frame/support", default-features = false }
+
+# Bridge Dependencies
+bp-xcm-bridge-hub-router = { path = "../../primitives/xcm-bridge-hub-router", default-features = false }
+
+[features]
+default = ["std"]
+std = [
+	"bp-xcm-bridge-hub-router/std",
+	"codec/std",
+	"frame-support/std",
+	"scale-info/std",
+]