Rely on the injectable type caster for `arel_table`

This API will require much less consuming code to change to accomodate
the removal of automatic type casting from Arel. As long as the
predicates are constructed using the `arel_table` off of an AR subclass,
there will be no changes that need to happen.
Extract an explicit type caster class
Fix failing tests
Pass a type caster when aliasing tables for joins
Remove all cases of manuallly wrapping `Arel::Nodes::Quoted`

This is no longer required now that we are injecting a type caster
object into the Arel table, with the exception of uniqueness
validations. Since it calls `ConnectionAdapter#type_cast`, the value has
already been cast for the database. We don't want Arel to attempt to
cast it further, so we need to continue wrapping it in a quoted node.
This can potentially go away when this validator is refactored to make
better use of `where` or the predicate builder.