LPS-46132 Consume the new social related methods in UserLocalService from the mentions portlet

As requested, I've generalized a little bit CustomSQL#keywords to accept an extra parameter to customize the way wildcards are used. Also, I've reused the existing finder where possible; the exception is when we are looking up users both by social relations and groups: in this case we need the union of both, but the findKeywords method returns the intersection (both SocialRelation and UsersGroups tables are included in the same JOIN clause).