createEvent: Only run dataTransfer workarounds in jsdom environments

[nifgraup]

What:

Fixes for browser based environments, not present when used with jest/jsdom.

Why:

createEvent has a workaround for missing event.dataTransfer objects as they don't exist in jsdom environments like jest #585 . Browser-based environments will have native DataTransfer objects and that should be used as the tests may rely on them being the real thing.

How:

A simple check to see if the workaround is needed.

Checklist:

• N/A[ ] Documentation added to the docs site
• I wish I could write a test case but this requires a test environment other than node.js/jest/jsdom [ ] Tests
• N/A [ ] TypeScript definitions updated
• [x] Ready to be merged

[nifgraup]

build failure is dealt with in #1346