Mostly cosmetics, except that `isolate_namespace` should be applied to the last
module in the chain.

Allow hyphenated names for `rails plugin new` generator

Unfortunately, the HashWithIndifferent access approach is insufficient
for our needs. It's perfectly reasonable to want to use keyword
arguments with Active Job, which we will see as a symbol keyed hash. For
Ruby to convert this back to keyword arguments, it must deserialize to a
symbol keyed hash.

There are two primary changes to the serialization behavior. We first
treat a HWIA separately, and mark it as such so we can convert it back
into a HWIA during deserialization.

For normal hashes, we keep a list of all symbol keys, and convert them
back to symbol keys after deserialization.

Fixes #18741.

Remaining are `limit`, `precision`, `scale`, and `type` (the symbol
version). These will remain on the column, since they mirror the options
to the `column` method in the schema definition DSL

The goal is to remove the type object from the column, and remove
columns from the type casting process entirely. The primary motivation
for this is clarity. The connection adapter does not have sufficient
type information, since the type we want to work with might have been
overriden at the class level. By taking this object from the column,
it is easy to mistakenly think that the column object which exists on
the connection adapter is sufficient. It isn't.

A concrete example of this is `serialize`. In 4.2 and earlier, `where`
worked in a very inconsistent and confusing manner. If you passed a
single value to `where`, it would serialize it before querying, and do
the right thing. However, passing it as part of an array, hash, or range
would cause it to not work. This is because it would stop using prepared
statements, so the type casting would come from arel. Arel would have no
choice but to get the column from the connection adapter, which would
treat it as any other string column, and query for the wrong value.

There are a handful of cases where using the column object to find the
cast type is appropriate. These are cases where there is not actually a
class involved, such as the migration DSL, or fixtures. For all other
cases, the API should be designed as such that the type is provided
before we get to the connection adapter. (For an example of this, see
the work done to decorate the arel table object with a type caster, or
the introduction of `QueryAttribute` to `Relation`).

There are times that it is appropriate to use information from the
column to change behavior in the connection adapter. These cases are
when the primitive used to represent that type before it goes to the
database does not sufficiently express what needs to happen. An example
of this that affects every adapter is binary vs varchar, where the
primitive used for both is a string. In this case it is appropriate to
look at the column object to determine which quoting method to use, as
this is something schema dependent.

An example of something which would not be appropriate is to look at the
type and see that it is a datetime, and performing string parsing when
given a string instead of a date.  This is the type of logic that should
live entirely on the type. The value which comes out of the type should
be a sufficiently generic primitive that the adapter can be expected to
know how to work with it.

The one place that is still using the column for type information which
should not be necessary is the connection adapter type caster which is
sometimes given to the arel table when we can't find the associated
table. This will hopefully go away in the near future.

The test added in 85465ed3 was passing
when the file was run on its own, but failing when the entire suite was
run since this test modifies the class and doesn't clean up.

It was not possible to create a new gem with a hyphenated name via the `rails plugin new` generator.

The naming guide of rubygems clearly says dashes should be used for gems that extend other gems. http://guides.rubygems.org/name-your-gem/

Collection associations would have already been validated, but singular
associations were not.

Fixes #18735.

This prevents a flood of warnings when generating a new scaffold.

Fix grammar in Qualified Constants section [ci skip]

New wording is based on the "cref" sentence earlier in the section.

[ci skip]

Improvements about schema dumping [ci skip]

Add a margin to body and padding to th, td in scaffold.css.

Add space to new css defs.

Doc: run bundle update after cloning Rails.

Update option to skip test in generators

Fixed AR::Relation#group method when argument is a SQL reserved keyword

Use kwargs in ActionController::TestCase and ActionDispatch::Integration HTTP methods

Non-kwargs requests are deprecated now.
Guides are updated as well.

`post url, nil, nil, { a: 'b' }` doesn't make sense.
`post url, params: { y: x }, session: { a: 'b' }` would be an explicit way to do the same

Preserve default format when generating URLs

Add fix for loading fixtures in engine tests (additional fix for #4971)

Conflicts:
	railties/lib/rails/generators/rails/plugin/templates/test/test_helper.rb

Module#const_defined? accepts constant paths in modern Ruby, we no longer
need our qualified_* extensions.

References #17845.

Fixes #18717