Don't trim excess whitespace in pg #columns_for_distinct

Fixes #16623 introduced by https://github.com/rails/rails/commit/3d5a2019bcccc6fb01bee4811ca669f4383edb51
Fix guide anchor generation logic.

This could use in any translation because it's not limited to `[^a-z0-9]`.

Verify after this change, all guides still have same anchors.

[Robin Dupret & Juanito Fatas]
Merge pull request #16649 from Agis-/pg-columns-for-distinct

Fix postgresql adapter #columns_for_distinct trimming whitespace it shouldn't
CHANGELOG & improvements to #16649

* Require either FIRST or LAST qualifier for "NULLS ..."
* Require whitespace before "NULLS ..."
Merge pull request #16667 from JuanitoFatas/patch/anchor-generation

Fix guide anchor generation logic.
show stats for app/jobs
Raise ActiveJob::SerializationError when cannot serialize job arguments
Describe web-console in the release notes [ci skip]

I put a more up-to-date description of Web Console in the release notes.
I'm not really happy with the language, so if you guys can help me with
that I'll be grateful :)
Merge pull request #16671 from cristianbica/aj-raise-serialization-error

Raise ActiveJob::SerializationError when cannot serialize job arguments
Merge pull request #16674 from gsamokovarov/describe-web-console

Describe web-console in the release notes
[ci skip] Added documentation for has_many extension parameter
Grammer and spelling pass on web console release note. [CI SKIP]
Merge pull request #16676 from tgxworld/web_console_release_note_fixes

Grammer and spelling pass on web console release note. [CI SKIP]
Merge pull request #16675 from tomkadwill/has_many_documenting_extension_param

[ci skip] Added documentation for has_many extension parameter
Merge pull request #16673 from y-yagi/update_statistics_rake

show stats for app/jobs
Fix a few typos [ci skip]
Some tweaks to the development set-up guide

* Remove the libxml2 and libxslt part ; Nokogiri ships now with these
  libraries bundled.
* Add the missing installation instructions for either Arch Linux,
  FreeBSD or Mac OS X.
* Use the new `pkg install` syntax over `pkg_add -r` for FreeBSD 10+
  users.
* Point to the up-to-date version of PostgreSQL as for the BSD port.
* Make the platform installation instructions order consistent
  throughout the guide.
* Remove useless duplicated links to Homebrew's home.

[ci skip]
Whoops, duplicated word [ci skip]