Implement polyfill for globalThis (v11)

[tomduncalf]

What, How & Why?

See https://github.com/realm/realm-js/pull/4653, this fixes one additional usage in v11

☑️ ToDos

• [x] 📝 Changelog entry
• [ ] 📝 Compatibility label is updated or copied from previous entry
• [ ] 🚦 Tests
• [ ] 🔀 Executed flexible sync tests locally if modifying flexible sync
• [ ] 📱 Check the React Native/other sample apps work if necessary
• [ ] 📝 Public documentation PR created or is not necessary
• [ ] 💥 Breaking label has been applied or is not necessary

If this PR adds or changes public API's:

• [ ] typescript definitions file is updated
• [ ] jsdoc files updated
• [ ] Chrome debug API is updated if API is available on React Native

[tomduncalf]

Blocked waiting on v11 to be rebased on master