fix: Work around vue-apollo@3 bug

What does this MR do?

fix: Work around vue-apollo@3 bug

While GitLab UI doesn't directly use vue-apollo@3, the FilteredSearch component can generate errors in projects which do (like GitLab).

The problem is that under certain circumstances, vue-apollo invokes a component's provide option method during the its beforeCreate lifecycle event. This is too early, and breaks the expectation that props can be referenced in a component's provide option method.

The workaround here is to return a function that returns the component's prop value, rather than the plain value itself. This works because the prop is read lazily, when the descendant component calls the provided function, by which time the ancestor's props will have been initialised.

Previous description

When consuming filtered_search_bar_root.vue in gitlab, I was getting a consistent error

cannot read suggestionsListClass of undefined

Upon investigation with @peterhegman , we discovered that if returning the value as a function fixed this.

1. We have no idea why this isnt erroring in other parts of the application
2. There is limited documentation on Vue specifying the use of provide as a function.
3. I dont see suggestionsListClass or alignSuggestions being used in the gitlab or the gitlab-ui codebase (i could be missing something).
4. Calculating the portalName can be moved to a computed property or something like that because were just passing this down as props.

Coming to think of it maybe those arent needed and we can refactor the use of these provide attrributes?

Does this MR meet the acceptance criteria?

Conformity

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• Added the ~"component:*" label(s) if applicable.

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
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Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.