Allow ComputedType to be passed to the set method on ABI types like Uint

[barnjamin]

Problem

At the moment the only way to set something like the return value of a subroutine or an array element as the value of an ABI type is to use the store_into method or the use method. Neither of these are obvious to someone without looking up exactly what is available to them.

Solution

Allow the set method to accept a ComputedType and call the store_into method internally.

This allows for a more natural syntax

#...

(v := abi.Uint64()).set(arr[i.load()])

# Or for a tuple

(acct := abi.String()).set(tpl[0])
(balance := abi.Uint64()).set(tpl[1])