fix: Ensure that combobox empty state is rendered when items arent directly provided to the combobox

[LFDanLu]

Closes #8708

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

Test the RAC combobox async loading story and type in string that doesnt match (e.g. aaaaaaaa). "No Results" message should appear.

Try the same with the S2 async combobox as well

🧢 Your Project:

RSP

[rspbot]

Build successful! 🎉

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• View the S2 storybook
• View the documentation
• View the S2 docs

[LFDanLu]

opted to add renderEmptyState in the reusable example, but that means there is a slight item height increase when typing in the async example and it renders the emptyState since that example doesn't use MyItem. If we are fine with that example getting the red hover style I can change that too

[yihuiliao]

i think it's fine personally

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the documentation
• View the S2 docs

[LFDanLu]

If the ComboBox either uses defaultItems or has its items defined by the wrapped ListBox, useComboBoxState will return a ListCollection instead of a BaseCollection, resulting in a different way of calculating collection size. The below change makes sure the loaders aren't included in the keymap which should be fine since they aren't focusable. Ideally, we'd always use a BaseCollection though

[reidbarber]

LGTM