fix(useCombobox): dispatch on Enter keydown event

[silviuaavram]

What:

Call dispatch on Enter keydown.
Prevent event default (form submission) if menu is open.
Do not return highlightedIndex from reducer if menu is closed.
Fix the MUI example for useSelect on the docsite.

Why:
Fixes #1114.
Also to fix other potential issues.

How:
Fix the reducer for the useCombobox hook.
Add itemsAsObjects to the MUI example useCombobox hook.
Check state.isOpen before returning a highlightedIndex in the Home/End actions.

Checklist:

• Documentation
• Tests
• TypeScript Types
• Flow Types
• Ready to be merged
  

[silviuaavram]

🎉 This PR is included in version 6.0.4 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[fabb]

Haha, this broke my workaround for the old behavior 😆
Don't get me wrong, thanks for fixing! Thankfully I had unit tests in place using @testing-library.
The funny thing was that the tests were green locally, but red on the CI server. It took me a while to find out that I locally had 6.0.2 installed, and the CI server installed 6.0.5 which already includes this fix... (yes, I'm using a package-lock.json file + run npm ci, but unfortunately this dependency is one that is hoisted via lerna and therefore bypasses the package-lock.json)

[silviuaavram]

How did you test that the submit event is not dispatched (if you did indeed manage to test it). @fabb

[fabb]

In my custom component that uses the downshift hooks, I have a few callback props that get called when some state changes (like onBlur, onSelectedItemsChanged, onInputValueChanged). In the jest tests I pass a jest mock for these props, and check how often the mock callbacks have been called and with which parameters.

My unit tests have a lot more lines than the actual implementation 😅