Maintain order of operations and resources

[mtdowling]

This commit updates service and operation shapes to maintain the order
in which operations and resources are defined in a Smithy model. Note
that resource lifecycle operation order is not maintained since those
are named operations that don't have any particular order in a model
like a list of operations, collectionOperations, or resources do.

To achieve this, I added a couple new helper methods to make copies of
Maps and Sets that maintains order.

Closes #591

[Baccata]

👍

[kstich]

Should there be associated spec updates with this, like with the recommendation to add members to the ends of their respective shapes?

[mtdowling]

I don't see this as something for the spec right now for a few reasons:

1. I think there's an implicit expectation about ordering here because these operations and resources are defined in lists which are inherently ordered.
2. Adding operations or resources in a recommended order isn't the intention here; this just guarantees maintaining order in the in-memory semantic model, and order is completely arbitrary and up to the modeler.
3. I think this is more of an "implementer's note" which could be added later if we discover it's necessary to explicitly mandate this detail of the semantic model.