Export drag and drop service methods

[chandlerprall]

Summary

Fixes #2372 by exporting the copy, move, and reorder drag-and-drop service methods. I tested by building EUI with this change and requireing the built package into node, verifying the three methods exist as expected.

Checklist

- [ ] Checked in dark mode
- [ ] Checked in mobile
- [ ] Checked in IE11 and Firefox
- [ ] Props have proper autodocs
- [ ] Added documentation examples
- [ ] Added or updated jest tests

• Checked for breaking changes and labeled appropriately
  - [ ] Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[thompsongl]

LGTM. Only question would be if we want to export these with less generic names...

[chandlerprall]

@thompsongl yeah that's a good call; we don't have a strong precedent here (TBH not even a weak one). They don't need to be discoverable except through the docs, so I'm thinking something like dndCopy dndMove and dndReorder - what do you think?

pinging @snide @cchaos for your thoughts as well

[thompsongl]

No strong preference on what the names are. I think the dnd prefix works.

[snide]

I'd continue with the eui prefix if possible so folks know where it's coming from. euiDragDropCopy...etc.

[chandlerprall]

I've updated the method names to euiDragDrop*, and did so at their creation (previously was renaming them at the last export) so our docs would reflect the correct name.

[thompsongl]

Thanks!