Expands InternalExportDataProvider per dataverse-spi 2.1.0 and refactors the DDI exporter to utilize the new functionality

[landreev]

Please note that this is a draft! Also note that it's not going to build outside of my own environment at the moment, since it's configured with an unreleased version of dataverse-spi in the pom file. [edit: it builds now, by Jenkins, etc., with a published snapshot release of dataverse-spi]

What this PR does / why we need it:

Which issue(s) this PR closes:

• Closes #11405

Special notes for your reviewer:

Suggestions on how to test this:

Does this PR introduce a user interface change? If mockups are available, please link/include them here:

Is there a release notes update needed for this change?:

Additional documentation: