Feature: Add navigation.isLoading state to core/router store

[fabiankaegy]

What?

Adds a new navigation.isLoading state to the core/router interactivity store

Why?

Today the router only has the navigation.hasStarted and navigation.hasFinished states. These only get set if the loadingAnimation option is not set to false.

Because of this it is not possible to hide the global loading indicator whilst still knowing whether or not the router is currently loading something.

How?

Adds a new state to the store

[github-actions]

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Co-authored-by: fabiankaegy <fabiankaegy@git.wordpress.org>
Co-authored-by: michalczaplinski <czapla@git.wordpress.org>

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[github-actions]

Flaky tests detected in 4fe358e.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/12196351428
📝 Reported issues:

• [Flaky Test] Redirection after template creation #60678 in /test/e2e/specs/site-editor/site-editor-url-navigation.spec.js

[michalczaplinski]

This looks good to me. Thanks for the quick PR, @fabiankaegy.

We can now use this flag to add UI in #67181 to show a custom UI when the user is waiting for search results.

[luisherranz]

I believe this API needs more consideration for WP 6.8, but we can test it as it is until then.

I have added it to the WordPress 6.8 iteration, by the way.

[sirreal]

I unintentionally enabled auto-merge on this PR. Feel free to proceed as necessary if it needs to be reverted or needs additional changes.

[michalczaplinski]

I just noticed it after approving 🙂. No worries, we can try out the API while it's in Gutenberg.

It would also need some e2e tests.