Enable and fix "clean exit" tests

[kraenhansen]

What, How & Why?

This closes #4535 if the Realm.clearTestState is called.
It relies on realm/realm-core#7231 being merged and released.

To be honest, this doesn't feel like the "right" fix, since we have this problem not only with App instances, but any object backed by an "internal" returned from core.
These "internal" objects hold shared pointer references of C++ objects which protects JS values that it gets passed (such as functions passed through configs, etc).
The "internal" shared pointers only get reset when the wrapping JS object gets garbage collected, which in turn allows for the captured JS values to be garbage collected.
All of this introduce delays (JS values being garbage collected → freeing C++ objects → unprotecting JS values → JS values being garbage collected).

The "right" solution would be to find a better way to handle references to objects between JS and C++ that allows earlier garbage collection.

☑️ ToDos

• 📝 Changelog entry
• 📝 Compatibility label is updated or copied from previous entry
• 📝 Update COMPATIBILITY.md
• 🚦 Tests
• 📦 Updated internal package version in consuming package.jsons (if updating internal packages)
• 📱 Check the React Native/other sample apps work if necessary
• 💥 Breaking label has been applied or is not necessary

[kraenhansen]

Part of this PR was cherry-picked into #6571.

[kraenhansen]

Closing this since we believe the Realm.shutdown method introduced in #6571 would suffice for now.