Adding on top of the new builder pattern for creating XCM programs, I'm
adding some more APIs:
```rust
let paying_fees: Xcm<()> = Xcm::builder() // Only allow paying for fees
.withdraw_asset() // First instruction has to load the holding register
.buy_execution() // Second instruction has to be `buy_execution`
.build();
let paying_fees_invalid: Xcm<()> = Xcm::builder()
.withdraw_asset()
.build(); // Invalid, need to pay for fees
let not_paying_fees: Xcm<()> = Xcm::builder_unpaid()
.unpaid_execution() // Needed
.withdraw_asset()
.deposit_asset()
.build();
let all_goes: Xcm<()> = Xcm::builder_unsafe() // You can do anything
.withdraw_asset()
.deposit_asset()
.build();
```
The invalid bits are because the methods don't even exist on the types
that you'd want to call them on.
---------
Co-authored-by: command-bot <>
Added a proc macro to be able to write XCMs using the builder pattern.
This means we go from having to do this:
```rust
let message: Xcm<()> = Xcm(vec![
WithdrawAsset(assets),
BuyExecution { fees: asset, weight_limit: Unlimited },
DepositAsset { assets, beneficiary },
]);
```
to this:
```rust
let message: Xcm<()> = Xcm::builder()
.withdraw_asset(assets)
.buy_execution(asset, Unlimited),
.deposit_asset(assets, beneficiary)
.build();
```
---------
Co-authored-by: Keith Yeung <kungfukeith11@gmail.com>
Co-authored-by: command-bot <>
gupnik