Add MockApi::addr_make

[webmaster128]

Create a function that allows creating test addresses from arbitrary strings. As discussed in #1873.

E.g. in test code

let manager: Addr = api.addr_make("manager");
let user1: Addr = api.addr_make("Alice");
let user2: Addr = api.addr_make("Bob");

[DariuszDepta]

Just to confirm, because different name is in the title and in examples. Do we stick to the convention in Api and name it addr_make?

Additionally, in cosmwasm-vm::testing there is also MockApi defined. Do we need to add the same function also there?

[chipshort]

I talked about this with @webmaster128 a few minutes ago.
Ideally we would only add it on the MockApi, not the trait. That would prevent people from misusing it in contract code.
The only thing that might pose a problem is if e.g. multi-test passes the MockApi as &dyn Api somewhere to test code. Then you would not have access to the function.
If that's the case, we can add it to the trait with a default unimplemented!() impl and implement it for the MockApi.
If not, I prefer the first option.

[webmaster128]

Thanks. I updated the example to use the same name as the title. My motivation for the name is:

• Include addr as it creates an Addr
• Use it as a prefix similar to addr_humanize and addr_validate but If it is not in the trait, I don't have a strong opinion here
• Prefer "make" or "new" over "hash" because hashing is an implementation detail. We can also implement it as a lookup table. The user should not worry about how to get from their describer string to the actual address

But feel free to disagree with those points and wer find the best name.

Additionally, in cosmwasm-vm::testing there is also MockApi defined. Do we need to add the same function also there?

Good questions. This belongs to a related but different trait BackendApi. We can skip it for now and if we see the need, copy it over.