Should test both mysql adapters

Added test for `send_file_headers` called with nil content type

Run Beanstalkd integration tests in ActiveJob

Correctly dump composite primary key

String#strip_heredocs doesn't need Object#try anymore

Call to Object#try was removed with this pull request https://github.com/rails/rails/pull/21596

Example:

    create_table :barcodes, primary_key: ["region", "code"] do |t|
      t.string :region
      t.integer :code
    end

Some test cases are testing only mysql adapter. We should test mysql2
adapter also.

Remove `@connection` in `StatementPool`

`@connection` in `StatementPool` is only used for PG adapter.
No need for abstract `StatementPool` class.

Replaced `ThreadSafe::Map` with successor `Concurrent::Map`.

Correcting `NameError` error message in `mattr_reader` method. [ci skip]

Corrected numeric conversions output [ci skip]

The thread_safe gem is being deprecated and all its code has been merged
into the concurrent-ruby gem. The new class, Concurrent::Map, is exactly
the same as its predecessor except for fixes to two bugs discovered
during the merge.

Replace `#=>` with `# =>` [ci skip]

change test method name to the appropriate name

@rafaelfranca suggested in https://github.com/rails/rails/commit/f7c7bcd9c2a8b0e8c2840295d001d2d4dfd4cfae that code examples should display
the result after  `# =>` and not after `#=>`.

Fixed unclosed tags in kindle guide source [ci skip]

nodoc raw_write_attribute

Is this supposed to be public API? If so, I can document it instead.
📝

This can still be added to the middleware stack, but is really not
necessary.  I'll follow up with a commit that deprecates the constant

* pp:
  remove outdated comment
  all parameter parsing is done through the request object now.
  let the request object handle parsing XML posts
  remove setting request parameters for JSON requests
  remove the request parameter from `parse_formatted_parameters`
  do not instantiate a param parser middleware
  push the parameter parsers on to the class
  stop eagerly parsing parameters
  only wrap the strategy with exception handling
  pull `normalize_encode_params` up
  remove the `default` parameter from the parser method
  move parameter parsing to the request object

all parameter parsing is done on the request object now, so we don't
need to worry about at ParamParser middleware

The test request object will handle parsing XML posts now, so we don't
need to eagerly parse them in the test harness

Correcting `NameError` error message in `mattr_reader` method. Since this commit https://github.com/rails/rails/commit/7dfbd91b0780fbd6a1dd9bfbc176e10894871d2d, `NameError` includes attribute_name also in error message [ci skip]

 

The request object will automatically parse these in the
`parse_formatted_parameters` method, so we don't have to worry about it.

This is an instance method on the request object now so we don't need it
anymore

we don't actually need a param parser middleware instance since the
request object will take care of parsing parameters for us.  For now,
we'll just configure the parameter parsers on the request in this class.

Include interpolation values to translation_missing helper

Added test for `any` if called without specifying any format

The middleware stack is a singleton in the application (one instance is
shared for the entire application) which means that there was only one
opportunity to set the parameter parsers.  Since there is only one set
of parameter parsers in an app, lets just configure them on the request
class (since that is where they are used).