`relation.exists?` just wants to know if there is a result or not, does
not need the exact records matched. Therefore, an intermediate SELECT
query for eager loading is not necessary.

We can use `relation.last(index)[-index]` instead of loading all records
when using reversible order because `last` will call `reverse_order`.

Currently `last` with `offset` behaves incorrectly because `offset` can
not be reversed like `limit`. Therefore, `offset` should also be handled
like `limit`.

ref https://github.com/rails/rails/pull/22653

Make it clear that `exists?` can be chained onto a relation

Fixes #30315.

I don't think this is a good abstraction because the internal method is
used only if the relation need to be applied join dependency.

`relation.exists?` should reference correct aliases while joining tables
of has_many through associations.

This is preparation to respect parent relation's alias tracking for
fixing #30681.

Because `quoted_table_name` doesn't respect table alias. We should use
`arel_attribute` for that, so I added `column_name_from_arel_node` to
generate column name from an arel node.

This regression was caused by caa178c1. The block for
`set_inverse_instance` should also be passed to join dependency.

Fixes #30402.

This builds on top of 15e2da65.
now it also returns exact Ids which were not found which will be debugging simple.

A common source of bugs and code bloat within Active Record has been the
need for us to maintain the list of bind values separately from the AST
they're associated with. This makes any sort of AST manipulation
incredibly difficult, as any time we want to potentially insert or
remove an AST node, we need to traverse the entire tree to find where
the associated bind parameters are.

With this change, the bind parameters now live on the AST directly.
Active Record does not need to know or care about them until the final
AST traversal for SQL construction. Rather than returning just the SQL,
the Arel collector will now return both the SQL and the bind parameters.
At this point the connection adapter will have all the values that it
had before.

A bit of this code is janky and something I'd like to refactor later. In
particular, I don't like how we're handling associations in the
predicate builder, the special casing of `StatementCache::Substitute` in
`QueryAttribute`, or generally how we're handling bind value replacement
in the statement cache when prepared statements are disabled.

This also mostly reverts #26378, as it moved all the code into a
location that I wanted to delete.

/cc @metaskills @yahonda, this change will affect the adapters

Fixes #29766.
Fixes #29804.
Fixes #26541.
Close #28539.
Close #24769.
Close #26468.
Close #26202.

There are probably other issues/PRs that can be closed because of this
commit, but that's all I could find on the first few pages.

Without this fix, `JoinDependency` doesn't use a custom table alias:

```
% ARCONN=sqlite3 be ruby -w -Itest test/cases/relations_test.rb -n test_using_a_custom_table_with_joins_affects_the_wheres
Using sqlite3
Run options: -n test_using_a_custom_table_with_joins_affects_the_wheres --seed 14531

E

Error:RelationTest#test_using_a_custom_table_with_joins_affects_the_wheres:
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: posts.author_id: SELECT  "omg_posts".* FROM "posts" "omg_posts" INNER JOIN "authors" ON "authors"."id" = "posts"."author_id" WHERE "omg_posts"."title" = ? LIMIT ?
```

`arel_engine` is only used in `raise_record_not_found_exception!` to use
`engine.connection` (and `connection.visitor`) in `arel.where_sql`.

https://github.com/rails/arel/blob/v8.0.0/lib/arel/select_manager.rb#L183

But `klass.connection` will work as expected even if not using
`arel_engine` (described by `test_connection`). So `arel_engine` is no
longer needed.

The `find_each`, `find_in_batches` and `in_batches` APIs usually operate
on large numbers of records, where it's preferable not to load them all
into memory at once.

If the query cache is enabled, it will hold onto the query results until
the end of the execution context (request/job), which means the memory
used is still proportional to the total number of records. These queries
are typically not repeated, so the query cache isn't desirable here.

This reverts commit 3420a145, reversing
changes made to afb66a5a.

The delegation was needed since passing `relation` with
`relation.bound_attributes`. It should use `relation.arel` in that case.

If a connection adapter overrides `select_*` methods, query caching will
doesn't work. This patch changes `select_value` to `select_one` in
`Relation#exists?` to ensure query caching.

Fixes #29449.

Fixes #29025.

To ease to customize a relation for `exists?`.

This reverts commit a680a581, reversing
changes made to 842f67dd.

Reason: I can't resist to the joke, so better to keep it there
https://github.com/rails/rails/pull/28598#issuecomment-290945339.

silly method gets a silly doc fix, 
or I'm missing an even sillier joke and I'm about to get schooled.

BUT I'm pretty sure this is some serious Beaudrillard simulacrum, though.
I'm just doing my part to spread the gospel of Douglas Adams.

If the `index` exceeds a `limit`, simply return an empty result without
querying the database.

find and exists?

Some methods were added to public API in
5b14129d and they should be not part of
the public API.