Avoid growing copies of collections of known size

Motivation and Context

Improves the performance of building collections by allocating the expected size beforehand instead of letting the collection grow as we add elements. This trivial change has small, but noticeable, performance improvements in the benchmarks for RPCv2, but will also benefit other protocols

Before

Benchmark                              (protocol)  (size)  Mode  Cnt      Score     Error  Units
JsonMarshallerBenchmark.unmarshall  smithy-rpc-v2   small  avgt    5   1944.436 ±  21.069  ns/op
JsonMarshallerBenchmark.unmarshall  smithy-rpc-v2  medium  avgt    5   3209.297 ± 259.975  ns/op
JsonMarshallerBenchmark.unmarshall  smithy-rpc-v2     big  avgt    5  11061.383 ± 187.669  ns/op

And flamegraph snippet below

After

Benchmark                              (protocol)  (size)  Mode  Cnt      Score     Error  Units
JsonMarshallerBenchmark.unmarshall  smithy-rpc-v2   small  avgt    5   1821.490 ±  18.858  ns/op
JsonMarshallerBenchmark.unmarshall  smithy-rpc-v2  medium  avgt    5   3045.257 ± 239.893  ns/op
JsonMarshallerBenchmark.unmarshall  smithy-rpc-v2     big  avgt    5  10593.384 ± 113.698  ns/op

And flamegraph snippet below

Modifications

Testing

Screenshots (if appropriate)

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)

Checklist

[ ] I have read the CONTRIBUTING document
[ ] Local run of mvn install succeeds
[ ] My code follows the code style of this project
[ ] My change requires a change to the Javadoc documentation
[ ] I have updated the Javadoc documentation accordingly
[ ] I have added tests to cover my changes
[ ] All new and existing tests passed
[ ] I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
[ ] My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

[ ] I confirm that this pull request can be released under the Apache 2 license

aws / aws-sdk-java-v2

Avoid growing copies of collections of known size #5551