Subspace packWithVersionstamp vs pack

Hey, been reading through some code to start using Versionstamps in my code, and I noticed some interesting behavior with the two pack methods.

[Subspace#pack](https://github.com/apple/foundationdb/blob/170013d69b1e4893d990fcc5a0e09825bc9d8048/bindings/java/src/main/com/apple/foundationdb/tuple/Tuple.java#L360-L362) throws when there is an incomplete versionstamp in the tuple

and

[Subspace#packWithVersionstamp](https://github.com/apple/foundationdb/blob/170013d69b1e4893d990fcc5a0e09825bc9d8048/bindings/java/src/main/com/apple/foundationdb/tuple/Tuple.java#L443-L445) throws when there is no incomplete versionstamp in the Tuple

I ended up doing something like the following, and I saw other people have done the same. Was wondering why the api exists like this rather than having a single pack method that delegates to either of these options. Is there a different pattern I should be using here? Is there a case where you would want to call the pack/packWithVersionstamp method and have the exception get thrown?

```
if (tuple.hasIncompleteVersionstamp()) {
return subspace.packWithVersionstamp(tuple);
} else {
return subspace.pack(tuple);
}
```

Start by comparing the linked Subspace#pack and Subspace#packWithVersionstamp implementations in bindings/java/src/main/com/apple/foundationdb/tuple/Tuple.java. Determine the intended behavior for complete and incomplete versionstamps, then document the supported usage pattern and when each exception is expected.

Written by the indexing model from the issue text.