Follow up to #22642.

Follow up to #22642.

🎉 🍻

Still more to do. Please assist!

We know the query will return exactly one row for each entry in the
`ids` array, so we can do all the limit/offset calculations on that
array, in advance.

I also split our new ordered-ids behaviour out of the existing
`find_some` method: especially with this change, the conditionals were
overwhelming the actual logic.

Since the attributes API is new in Rails 5, we don't actually need to keep
the behavior of `attribute :point`, as it's not a breaking change.

The changelog entry for ApplicationRecord was a bit confusing. Thank you
guys for helping me get it in a better shape.

[ci skip]

Support passing the schema name as a prefix to table name in
`ConnectionAdapters::SchemaStatements#indexes`. Previously the prefix would
be considered a full part of the index name, and only the schema in the
current search path would be considered.

It was changed by mistake at 428d47ad

This reverts commit 4d06ea9a, reversing
changes made to e9d15072.

Reason: This will break oracle-enhanced, see
https://github.com/rsim/oracle-enhanced/blob/3c42131db82b64ac41645db3affc6e4650289df6/lib/active_record/connection_adapters/oracle_enhanced_adapter.rb#L1254

All public methods are tasks, so we need to move it to protected
visibility.

This test was failing when run on Windows using PostgreSQL. Depending on
the OS (and 32 vs 64 bit), this type could be a `BigNum`. We could loosen
the assertion to `Numeric`, but if the value is equal to the expected, and
responds to `bitlength` properly, who cares?

Unlike unix, the TZ variable on Windows does not look at a database. It is
always expected to be in the form {Standard Time
Abbreviation}{UTC-Offset}{Daylight Time Abbriviation}. This changes the
relevant tests to use the Windows form when run from Windows.

When this test was run on Windows, the database file would still be in
use, and `File.unlink` would fail. This would cause the temp directory to
be unable to be removed, and error out. By disconnecting the connection
when finished, we can avoid this error.

It's pretty common for folks to monkey patch `ActiveRecord::Base` to
work around an issue or introduce extra functionality. Instead of
shoving even more stuff in `ActiveRecord::Base`, `ApplicationRecord` can
hold all those custom work the apps may need.

Now, we don't wanna encourage all of the application models to inherit
from `ActiveRecord::Base`, but we can encourage all the models that do,
to inherit from `ApplicationRecord`.

Newly generated applications have `app/models/application_record.rb`
present by default. The model generators are smart enough to recognize
that newly generated models have to inherit from `ApplicationRecord`,
but only if it's present.

Fix white-space

Add test case demonstrating flags are received by the adapter

```
# before
DEPRECATION WARNING:               Time columns will become time zone aware in Rails 5.1. This
              still causes `String`s to be parsed as if they were in `Time.zone`,
              and `Time`s to be converted to `Time.zone`.

              To keep the old behavior, you must add the following to your initializer:

                  config.active_record.time_zone_aware_types = [:datetime]

              To silence this deprecation warning, add the following:

                  config.active_record.time_zone_aware_types << :time
```

```
# after
DEPRECATION WARNING: Time columns will become time zone aware in Rails 5.1. This
still causes `String`s to be parsed as if they were in `Time.zone`,
and `Time`s to be converted to `Time.zone`.

To keep the old behavior, you must add the following to your initializer:

    config.active_record.time_zone_aware_types = [:datetime]

To silence this deprecation warning, add the following:

    config.active_record.time_zone_aware_types << :time
```

We currently generate an unbounded number of prepared statements when
`limit` or `offset` are called with a dynamic argument. This changes
`LIMIT` and `OFFSET` to use bind params, eliminating the problem.

`Type::Value#hash` needed to be implemented, as it turns out we busted
the query cache if the type object used wasn't exactly the same object.

This drops support for passing an `Arel::Nodes::SqlLiteral` to `limit`.
Doing this relied on AR internals, and was never officially supported
usage.

Fixes #22250.

Some backends allow `LIMIT 1,2` as a shorthand for `LIMIT 1 OFFSET 2`.
Supporting this in Active Record massively complicates using bind
parameters for limit and offset, and it's trivially easy to build an
invalid SQL query by also calling `offset` on the same `Relation`.

This is a niche syntax that is only supported by a few adapters, and can
be trivially worked around by calling offset explicitly.

Even though this means more things to change when we bump after a
release, it's more important that our examples are directly copyable.

.. it also showed a deprecation warning, but we obviously needn't retain
that.

Apart from specific versioning support, our tests should focus on the
behaviour of whatever version they're accompanying, regardless of when
they were written.

Application code should *not* do this.

If we use a real version, at best that'll be an onerous update required
for each release; at worst, it will encourage users to write new
migrations against an older version than they're using.

The other option would be to leave these bare, without any version
specifier. But as that's just a variant spelling of "4.2", it would seem
to raise the same concerns as above.