SA: Create list of authzIDs earlier in NewOrderAndAuthzs

[jprenken]

Creating the list of authzIDs earlier in NewOrderAndAuthzs:

• Saves a for loop with duplicated code; we no longer need to range over two different slices, just one.
• Allows us to create the Order PB later, after more of the data collection logic, without interrupting it. This makes the order of operations slightly easier to follow.

[jsha]

nits:

The title of the PR doesn't give me a very clear idea what it does. Also, when we're touching a single discrete component we often (not universally) use that component as a prefix. I might say:

sa: create list of authzIDs earlier in NewOrderAndAuthzs

Also, the PR description should mention the movement of addReplacementOrder and getAuthorizationStatuses and have a short explanation of why it's clearer or better.

One thing I noticed related to the reordering: I think you should also be able to move statusForOrder above the res := &corepb.Order{ line too. That would be nice because you can replace res.Status = status with a field assignment inside the object creation (Status: status). And you could also combine the object literal with the return statement:

return &corepb.Order{
    Status: status,
    ...
}, nil

[jprenken]

One thing I noticed related to the reordering: I think you should also be able to move statusForOrder above the res := &corepb.Order{ line too. That would be nice because you can replace res.Status = status with a field assignment inside the object creation (Status: status).

Since statusForOrder requires an Order as an argument, I'd need to modify it to remove that requirement - a much bigger change that I didn't intend to take on with this PR.

[aarongable]

LGTM % Phil's comment.