Make banker.SendCoins take variadic Coin argument

[leohhhn]

Description

As the title says. Instead of having to build a slice each time you want to send coins, I propose we change the banker API to take in a variadic Coin argument.

Before:
func (ba bankAdapter) SendCoins(from, to Address, amt Coins)

After:
func (ba bankAdapter) SendCoins(from, to Address, amts ...Coin)

Here is the code.

[thehowl]

Note, the Coin and Coins type are missing many useful methods and constructors from their original form in tm2/pkg/std: https://github.com/gnolang/gno/blob/master/tm2/pkg/std/coin.go

IMO a better approach is to add better constructors for the types; using the Coins type is useful as it has useful methods to do logic on coins

[leohhhn]

I was more referring to the fact that when you want to send a single coin with the banker, you always need to pack it inside the Coins struct, which can get a bit annoying. Example:

realmAddr := std.CurrentRealm().Addr()
coinToSend := banker.GetCoins(realmAddr).AmountOf("ugnot")
banker.SendCoins(realmAddr, to, std.Coins{{ "ugnot", coinToSend }})

----

// bit nicer if:
banker.SendCoins(realmAddr, to, std.Coin{"ugnot", coinToSend})

// and can do
coins := std.Coins{...}
banker.SendCoins(realmAddr, to, coins...)

The other option is what you are suggesting, and that is adding the NewCoins constructor, which takes in a variadic Coin arg. 🤷

BTW, I am working on a small PR to introduce some more functionality to Coins/Coin in Gno by porting some stuff from coin.go.

[thehowl]

Yeah, I get you, what I'm saying is that Coins is a useful type and maybe we should tackle the underlying issue here by making its constructors useful.

[leohhhn]

Solution for this was to implement a variadic constructor for the Coins type. Implemented in #2104