Enhance docs for update_attribute [ci-skip]
use method_defined? to check whether or not a method is defined
Merge pull request #14364 from why-el/better-docs-for-update-attribute

Enhance docs for update_attribute [skip ci]
Fix a grammatical error in the i18n guide [ci skip]
Merge pull request #14366 from sukolsak/grammar

Fix a grammatical error in the i18n guide
only write the jar if the response isn't committed

when streaming responses, we need to make sure the cookie jar is written
to the headers before returning up the stack. This commit introduces a
new method on the response object that writes the cookie jar to the
headers as the response is committed.  The middleware and test framework
will not write the cookie headers if the response has already been
committed.

fixes #14352
just ask the response for the commit status, we do not need to ask the jar
use the body proxy to freeze headers

avoid freezing the headers until the web server has actually read data
from the body proxy.  Once the webserver has read data, then we should
throw an error if someone tries to set a header
Use Sqlite3 adapter in examples

Two bits of example code use sqlite as an adapter, which doesn't exist.
Using the code verbatim will raise a LoadError exception:

    ActiveRecord::Base.establish_connection(
      "adapter"  => "sqlite",
      "database" => "db.sqlite"
    )
    # => LoadError: Could not load 'active_record/connection_adapters/sqlite_adapter'...

Considering this is code a lot of people new to Rails might be running,
it's especially confusing.

Closes #14367 [ci skip]