make xcm_config public

[zqhxuyuan]

@KiChjang acala use xcm-emulator which mock real runtime, so previous it use kusama_runtime::XcmConfig. as #4644 changed, we need make xcm_config public, otherwise there're error like: module xcm_config is private.

https://github.com/AcalaNetwork/Acala/blob/9dfa889afea18b4dbff49f3e7fef3e26064fcb91/runtime/integration-tests/src/relaychain/kusama_test_net.rs#L31-L34

decl_test_relay_chain! {
	pub struct KusamaNet {
		Runtime = kusama_runtime::Runtime,
		XcmConfig = kusama_runtime::XcmConfig, // 🔥
		new_ext = kusama_ext(),
	}
}

the xcm-simulator in polkadot code base don't have this problem because it use mock XcmConfig. but parachain integration test need use real instead mock XcmConfig.

another question, should we move other xcm related config, such as cumulus_pallet_xcm::Config,cumulus_pallet_xcmp_queue::Config, cumulus_pallet_dmp_queue::Config to xcm_config? or just leave it alone?

[KiChjang]

should we move other xcm related config, such as cumulus_pallet_xcm::Config,cumulus_pallet_xcmp_queue::Config, cumulus_pallet_dmp_queue::Config to xcm_config? or just leave it alone?

Yes, I simply haven't gotten around to it yet.

[KiChjang]

bot merge