Fix group type views handler mapping for search api

Problem/Motivation

Currently when you have a search api index for group entities you get an error when you filter a view by group type. Search api has a standard views mapping for entities in _search_api_views_handler_mapping(). Group types (like node types) require a special type of handler mapping to fix this.

Proposed resolution

Implement hook_search_api_views_handler_mapping_alter() to add the correct handler mapping for group types in search api views.

Remaining tasks

User interface changes

API changes

Data model changes