Fix toJSON behaviour for Dictionary on JSC pre-v11 (fixes #4658)

[tomduncalf]

What, How & Why?

This fixes the behaviour of toJSON on objects with Dictionary fields on JSC, reported in #4658.

Before this fix, Dictionary fields would incorrectly not be converted to JSON, resulting in an exception if a field of the Dictionary of the JSONified object was modified, as it would try to write to the Realm outside of a write transaction.

The root cause of this is similar to #4541, in that Proxy objects do not seem to be properly "transparent" on JSC – in this case, instanceof Realm.Dictionary would return false for a proxied Dictionary, whereas it should return true (as JS Proxy objects are supposed to be totally transparent). This should be fixed with JSI/Hermes.

I searched the codebase for anywhere else that might be affected by this bug and couldn't see anywhere.

☑️ ToDos

• 📝 Changelog entry
• 📝 Compatibility label is updated or copied from previous entry
• 🚦 Tests
• 🔀 Executed flexible sync tests locally if modifying flexible sync
• 📦 Updated internal package version in consuming package.jsons (if updating internal packages)
• 📱 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

[takameyer]

@tomduncalf Looks like we need to publish @realm/common in order for the tests to run

[tomduncalf]

Yep, it's a slightly annoying set up @takameyer (will be fixed if realm becomes its own package) – I usually wait for the code to be approved before publishing it, then rerun with tests, as I'm not sure how easy unpublishing is if there's a change requested

[takameyer]

@tomduncalf oh yeah...that is a bit annoying. And the change by itself in a PR doesn't really bring much, as it's very dependent on the other code being written. We will just have to wait for that wonderful world where realm is also a package.

[takameyer]

LGTM