Add a data alteration for indexing the viewed entity

With entity_view(), there is now an easy way to index the entity completely, like it would be displayed to a user. This might in many cases provide the most accurate search results and is therefore a good candidate for a future data alteration.
The plugin would probably just prompt the user to select a view mode and would then add a fulltext field with the complete viewed entity as HTML.
Pretty simple but potentially a great feature.