fix(theme-classic): wrap item content when there's no link

[sarahdayan]

We use CSS grids to display items in columns, meaning the grid algorithm always tries to render content into columns. For this reason, we need to make sure the HTML structure is always the same. This means you now always need to either wrap the item within aa-ItemWrapper OR aa-ItemLink.

This PR moves the grid display on aa-ItemWrapper and aa-ItemLink, and updates the documentation, demos and plugins to reflect the change.

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@algolia/autocomplete-example-github-repositories-custom-plugin	Configuration
@algolia/autocomplete-example-playground	Configuration
@algolia/autocomplete-example-query-suggestion-with-categories	Configuration
@algolia/autocomplete-example-query-suggestions-with-hits	Configuration
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@algolia/autocomplete-example-react-renderer	Configuration
@algolia/autocomplete-example-recently-viewed-items	Configuration
@algolia/autocomplete-example-starter	Configuration

[francoischalifour]

We can merge once we remove the unused Fragment imports.