feat(next-app-router): listen to external URL changes

[aymeric-giraudet]

Fixes #6077

Summary

The App Router does not have events like the Pages router had, so we didn't implement a way to listen to external URL changes yet.

Result

The way to go is to use useEffect for that, as stated on their docs

I externalised everything into a hook to make the code easier to read and more focused, and to allow to do ISR / static generation more easily in the future (useSearchParams makes the page opt-out of such features)

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 6133c9d:

Sandbox	Source
react-instantsearch-app	Configuration
example-react-instantsearch-default-theme	Configuration
example-react-instantsearch-next-app-dir-example	Configuration
example-vue-instantsearch-default-theme	Configuration

[Haroenv]

same remark about tests, but that makes sense for now still as it's "beta" and we have it as a remaining task to figure out how to test this

[RobinGiel]

Is there a flag I can use to use this feature? because this push gave me issues with intercepted routes where the URL changes but no changes are needed from instant search. In the use case when the URL is used to just open a Modal for example no update is needed