Add loading indicator to combo box control author selector

[adamsilverstein]

This PR is a rework of the effort in #27865 - see that ticket for additional details.

Testing instructions

1. Create a large number of editors (see below for command).
2. Load a page in the editor
3. Open DevTools and throttle network connections to a 3G speed to slow down the rest API responses
4. Click the author to edit, then try typing in part of a user name

Expected results:

• A spinner is shown while the search callback executes
• the "No items found' string only shows when the search completes (and no items are found)

Helpful wp-cli commands for testing:

Generate many users to test searching: wp user generate --role=editor --count=100
Delete test users: wp user delete $(wp user list --role=editor --field=ID) --reassign=2

[adamsilverstein]

Note: the drop-down shows "No items found." during the search, a bug clearly visible currently (before this PR) when throttling the search callback.

[github-actions]

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Co-authored-by: adamsilverstein <[email protected]>
Co-authored-by: Mamaduka <[email protected]>

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[adamsilverstein]

I updated the PR to avoid showing "No items found" string while the results are still loading.

[Mamaduka]

Typo?

[adamsilverstein]

ha, this was me trying to get my build working and not seeing changes. will revert!

[Mamaduka]

The SuggestionsList component is shared, which is why we're passing the isLoading prop, correct?

[adamsilverstein]

right

[Mamaduka]

Thanks, @adamsilverstein!

My suggestion is to limit new loading state changes to the ComboboxControl. The FormTokenField component is a bit tricky, as input and tokens can wrap on multiple lines. So, I'm not sure if the spinner suffix design will work for it.

Do you mind including a screenshot or screencast in the PR description?

Hopefully, the v2 design will account for the loading state of #64086.

cc @WordPress/gutenberg-components

[adamsilverstein]

My suggestion is to limit new loading state changes to the ComboboxControl. The FormTokenField component is a bit tricky, as input and tokens can wrap on multiple lines. So, I'm not sure if the spinner suffix design will work for it.

Thanks for the review.

I will add some screenshots/screencasts to show what this change does (when I am back at my desk Friday). I can also take a look at other consumers of the component to make sure they are unaffected. The main goal of the change here is to avoid showing "No items found" string while the (author) search is underway. Since it isn't directly related to adding a spinner, I can break it out into a follow up PR and we can explore the issue separately.

[Mamaduka]

I think it's okay to change the SuggestionsList here, but let's avoid adding the isLoading prop to the FormTokenField. This way we can focus only on ComboboxControl improvements.