Support SQL sanitization in AR::QueryMethods#order

Add support for sanitizing arrays in SQL ORDER clauses.

This is useful when using MySQL `ORDER BY FIELD()` to return records in
a predetermined way.

```ruby
  Tag.order(['field(id, ?', [1,3,2]].to_sql
  # => SELECT "tags".* FROM "tags"   ORDER BY field(id, 1,3,2)
```

Prior to this, developers must be careful to sanitize `#order` arguments
themselves.