Fix Merge Conflicts after v3 -> v4 merge in petesong/stj branch

[peterrsongg]

Description

This change is just the code changes required to fix merge conflicts after rebasing petesong/stj on v4-development. The main things were the IsDateTime turning into IsTimeStamp, then the changes to s3 exception unmarshalling, and the removal of Amazon.Runtime.Internal.Transform.CustomMarshallTransformations.ConvertDateTimeToEpochMilliseconds in the generator.

Motivation and Context

Testing

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

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