Don't retain state across distinct-but-similar expanders

[vdonato]

📚 Context

It turns out that #4258 is caused by what seems to be a really fun bug --
distinct expanders sometimes look so similar that react's diffing algorithm
decides that the two elements are the same (but with different props), and so
the state of the useState hook is retained across two distinct expanders 🤯

The fix for this is to simply add a useEffect dependency on the hook currently
watching for default expanded state changes so that the expander's state is also
reset when its label changes.

• What kind of change does this PR introduce?

  • Bugfix

🧠 Description of Changes

• Fix expander state being incorrectly retained for distinct expanders by
  adding a useEffect dependency

• Added an e2e test for this behavior

  • This is a visible (user-facing) change

🧪 Testing Done

• Added/Updated e2e tests

🌐 References

• Issue: Closes Expander state is incorrectly shared by distinct expanders #4258

[mayagbarnes]

👍🏼