Clearing index data does not delete data/table for multivalue filterable attributes

Problem/Motivation

When clearing index data this module will currently delete and recreate the search_index table, but it does not do the same thing for tables that get created when you add a multi-value filterable attribute.

Steps to reproduce

Create an index, specify a multi-select entity relationship field as a filterable attribute and then index data. Then clear index and see that the search_index table has been wiped clean (and all field columns removed too) and then check the table for the multi value filterable attribute, the table will still be there and will still have all of it's data.

Proposed resolution

In dropCollection you should likely drop relation tables too.

Remaining tasks

User interface changes

API changes

Data model changes