Pass connection rather than alias_tracker

Fix handling of positional url helper arguments when format is false

There is no need to subtract one from the path_params size when there is
no format parameter because it is not present in the path_params array.

Fixes #17819.

Because we're only using the `connection` so passing the entire tracker
isn't unnecessary.

Eventually only the `connection` will be passed to `add_constraints`
with later refactoring but curretly that's not possible because of
`construct_tables` method.

[guides] Fix method name inconsistency in a mailer example

[ci skip]

Use redis protocol

Add AC::Parameters#to_unsafe_h

Closes #17965, #17968

[Godfrey Chan, Miklós Fazekas]

I'm not sure what's the use case for this, but apparently it broke some apps.
Since it was not the intended result from #16210 I fixed it to not raise an
exception anymore. However, I didn't add documentation for it because I don't
know if this should be officially supported without knowing how it's meant to
be used.

In general, validations should be side-effect-free (other than adding to the
error message to `@errors`). Order-dependent validations seems like a bad idea.

Fixes #18002

See 63462ec9

Make AC::Params.permit_all_parameters thread safe

Fix default queue name prefix delimiter

Now displays as underscore, and not an empty string, when converted from markdown to HTML.
Escaped the underscore per http://daringfireball.net/projects/markdown/syntax#em
Fixes rails/rails#18009

English fix [ci skip]

As suggested in #16299([1]), this method should be a new public API for
retrieving unfiltered parameters from `ActionController::Parameters`
object, given that `Parameters#to_hash` will no longer work in Rails
5.0+ as we stop inheriting `Parameters` from `Hash`.

[1]: https://github.com/rails/rails/pull/16299#issuecomment-50220919

As discussed in #16299[1], this attribute is not thread safe and could
potentially create a security issue.

[1]: https://github.com/rails/rails/pull/16299#discussion_r15424533

Remove custom errors page section from the guides [ci skip]

https://github.com/rails/rails/commit/39542fba54328ca048fb75a5d5b37f8e1d4c1f37#commitcomment-8938379

Fix ProtocolViolation/bind message for polymorphic + pluck or group+calc

Update guides with info about vendor/assets [ci skip]

fixes #17893

[ci skip]

Fix undesirable RangeError by Type::Integer. Add Type::UnsignedInteger.

Refactor `quoted_date`

This reverts commit b0e7278d, reversing
changes made to 785d04e3.

This is not true. It is a bug and we will fix in the latest 4.0.x
release.

Move microseconds formatting to `AbstractAdapter`.

Add foreign_type option for polymorphic has_one and has_many.

[ci skip] fix typo in MessageVerifier#verify docs

Adding information about 'allow_nil' option for 'numericality' [ci skip]

Add guides for `required` model generator option

Related to this PR #16062

[ci skip]