Upgrades prettier to the latest version, and auto-corrects files with
yarn prettier-all-save

The diffs all seem to stem from formatting changes in brackets within
template literals. Nothing major.

Relevant changelogs here:

https://prettier.io/blog/2019/04/12/1.17.0.html
https://prettier.io/blog/2019/06/06/1.18.0.html

Add changelog file

An instance of i18n which required sprintf was not handled correctly
and has been fixed in this commit.

Further to this, i18n was applied to
  app/assets/javascripts/new_branch_form.js
but needed to be removed as the i18n was too vague.

A note has been made to follow up on this file.

This is one of many MRs opened in order to improve the overall
internationalisation of the GitLab codebase.

This commit only targets Vanilla JS files.

i18n documentation
https://docs.gitlab.com/ee/development/i18n/externalization.html

Remove references to the vendored copies of At.js and jquery.carat
as well as the legacy rails wrapper gem.

This engine was replaced with CommonMarker in 11.4, it was deprecated
since then.

Added "cancel" comment button for inline diff notes for commits

Removed the button and associated tests form notes
on Issues and Merge request page.

Partially addresses #47006.