Add JavaScript test coverage for the SharePoint autocomplete widget and declare its library dependencies

Problem/Motivation

The o365_sharepoint_field autocomplete widget ships a client-side behavior (Drupal.behaviors.o365SharePointSearchAutocomplete in js/o365_sharepoint_field.autocomplete.js) that, on selecting an autocomplete result, copies the selected item's hitId and driveId into the hidden .o365-sharepoint-hit-id and .o365-sharepoint-drive-id fields. This behavior currently has no automated test coverage.

While adding a test, two things surfaced:

1. The o365_sharepoint_field/autocomplete library uses the jQuery, Drupal and drupalSettings globals but does not declare core/jquery, core/drupal or core/drupalSettings as dependencies. It only works today because the widget happens to attach core/drupal.ajax alongside it, which pulls those globals in transitively. If that ever changes, the behavior breaks silently.
2. There was no way to exercise the behavior in a browser test, because the widget only renders its markup when AuthenticationService::checkForOfficeLogin() returns TRUE (which requires an active Microsoft 365 login and is not reliably reproducible in a functional-JS test).

Steps to reproduce (dependency issue)

Attach only o365_sharepoint_field/autocomplete to a page (without core/drupal.ajax) and select an autocomplete result — the behavior throws because jQuery/Drupal are undefined.

Proposed resolution

• Declare the missing dependencies on the autocomplete library:
  

  dependencies:
    - core/jquery
    - core/drupal
    - core/drupalSettings

• Add a FunctionalJavascript test (SharePointAutocompleteBehaviorTest) that verifies selecting an autocomplete result populates the hidden hit-id/drive-id fields.
• Add a small, hidden test-support module (o365_sharepoint_field_test, hidden: true) that renders the same widget markup and attaches only the module's own library — so the test both exercises the real shipped JS and guards against the library dependencies regressing, without needing a Microsoft 365 login.

Remaining tasks

• Review the merge request.
• Confirm the GitLab CI pipeline (incl. the new functional-javascript job) passes.