Refer to a stable release of SDoc

Fix yaml deserialization of ActiveSupport::Duration

Use `serialize_entry` throughout and introduce `serialize_entries`.

Closes #31886
Fixes #31884

* PERF: Recover marshaling dump/load performance

This performance regression which is described in #30680 was caused by
f0ddf87e due to force materialized `LazyAttributeHash`.

Since 95b86e57, default proc has been removed in the class, so it is no
longer needed that force materialized.

Avoiding force materialized will recover marshaling dump/load
performance.

Benchmark:

https://gist.github.com/blimmer/1360ea51cd3147bae8aeb7c6d09bff17

Before:

```
it took 0.6248569069430232 seconds to unmarshal the objects

Total allocated: 38681544 bytes (530060 objects)

allocated memory by class
-----------------------------------
  12138848  Hash
  10542384  String
   7920000  ActiveModel::Attribute::Uninitialized
   5600000  ActiveModel::Attribute::FromDatabase
   1200000  Foo
    880000  ActiveModel::LazyAttributeHash
    400000  ActiveModel::AttributeSet
        80  Integer
        72  ActiveRecord::ConnectionAdapters::SQLite3Adapter::SQLite3Integer
        40  ActiveModel::Type::String
        40  ActiveRecord::Type::DateTime
        40  Object
        40  Range

allocated objects by class
-----------------------------------
    250052  String
    110000  ActiveModel::Attribute::Uninitialized
     70001  Hash
     70000  ActiveModel::Attribute::FromDatabase
     10000  ActiveModel::AttributeSet
     10000  ActiveModel::LazyAttributeHash
     10000  Foo
         2  Integer
         1  ActiveModel::Type::String
         1  ActiveRecord::ConnectionAdapters::SQLite3Adapter::SQLite3Integer
         1  ActiveRecord::Type::DateTime
         1  Object
         1  Range
```

After:

```
it took 0.1660824950085953 seconds to unmarshal the objects

Total allocated: 13883811 bytes (220090 objects)

allocated memory by class
-----------------------------------
   5743371  String
   4940008  Hash
   1200000  Foo
    880000  ActiveModel::LazyAttributeHash
    720000  Array
    400000  ActiveModel::AttributeSet
        80  ActiveModel::Attribute::FromDatabase
        80  Integer
        72  ActiveRecord::ConnectionAdapters::SQLite3Adapter::SQLite3Integer
        40  ActiveModel::Type::String
        40  ActiveModel::Type::Value
        40  ActiveRecord::Type::DateTime
        40  Object
        40  Range

allocated objects by class
-----------------------------------
    130077  String
     50004  Hash
     10000  ActiveModel::AttributeSet
     10000  ActiveModel::LazyAttributeHash
     10000  Array
     10000  Foo
         2  Integer
         1  ActiveModel::Attribute::FromDatabase
         1  ActiveModel::Type::String
         1  ActiveModel::Type::Value
         1  ActiveRecord::ConnectionAdapters::SQLite3Adapter::SQLite3Integer
         1  ActiveRecord::Type::DateTime
         1  Object
         1  Range
```

Fixes #30680.

* Keep the `@delegate_hash` to avoid to lose any mutations that have been made to the record

These are internally used only.

[ci skip]

These classes are internally used only.

Follow up of 16b92eed

I'm not sure cause, but due to the influence of `gem clean`, the expected
gem seems not to be installed correctly.
In order to avoid a test failure due to this, I fixed that `gem clean` not be executed.
Ref: https://github.com/travis-ci/travis-ci/issues/2518#issuecomment-121168856

This is a workaround. If Travis fixes something, please revert this.

Removed "private" generators from command list.

Allow ActiveStorage::Blob#service_url to pass addition options to service.url

ActiveStorage: use the full class name for the JSON coder

Use Oracle enhanced adapter `release52` to support Rails `5-2-stable`

This reverts commit ac74e2c5, reversing
changes made to ffdb0613.

Backport #31838 to 5-2-stable

Fix `as` attribute value for preload link

[Eileen M. Uchitelle & bogdanvlviv]

README in 5-2-stable should point files and path to 5-2-stable instead of master branch.

Disable CSP by default

Before this patch, to be able to use webpacker and webconsole we were
defining an used default in the script-src policy. White we don't
implement the automatic nonce approach defined in
https://github.com/rails/rails/issues/31689 it is better to not have any
default configuration in Rails 5.2.

Add ContentSecurityPolicy to list of middleware

Document in the guides the new middleware added in #31162
[ci skip]

Update rails-ujs readme

Allow @ in X-Request-Id header

yarnpkg: correct exec syntax

It is not a test case.

It makes sense to be as strict as possible
with headers from the outside world,
but allowing @ to support Apache's mod_unique_id
(see #31644) seems OK to me

Link to W3C reference was broken, this uses the latest URL, along with HTTPS.

Dump correctly index nulls order for PostgreSQL

Avoid extra calls to to_s