Support ERC-20 xcm transfer

[zqhxuyuan]

following #2165. Current Erc20 token withdraw operation not support in module_currencies, that'll cause xcm transfer failed in our side.

Acala/modules/currencies/src/lib.rs

Line 375 in 0ae648f

CurrencyId::Erc20(_) => Err(Error::<T>::Erc20InvalidOperation.into()),

[zqhxuyuan]

Karura send erc20 to Sibling, Sibling will take (1, 2000, Erc20) as foreign asset, not erc20
Sibling send (1, 2001, Erc20) to Karura, Karura will take it as foregin asset too.
Sibling send (1, 2000, Erc20) to Karura, Karura will take it as Erc20.

So, Asset-registry need support Erc20, or else there'll be none matched item in Trader:

Acala/modules/asset-registry/src/lib.rs

Lines 598 to 599 in ded6de5

	if let Some(CurrencyId::ForeignAsset(foreign_asset_id)) =
	Pallet::<T>::location_to_currency_ids(multi_location.clone())

[zqhxuyuan]

when Sibling transfer (1, 2000, Erc20) to Karura, xcm execution error in Karura side:

2022-06-02 20:44:42.055 TRACE tokio-runtime-worker xcm::execute_xcm_in_credit: [Parachain] 
result: Err(ExecutorError { index: 0, xcm_error: FailedToTransactAsset("RealOriginNotFound"), weight: 600000000 })