Resolve "Toggle file comments in merge request does not update toggle buttons"

Closes #48237 and #48537

See merge request gitlab-org/gitlab-ce!20452

* master: (38 commits)
  Update bitbucket.md to fix typo and small grammar touchups.
  Update time_helper.rb to fix output for exact minutes.
  Document update for GitLab Pages users.
  Support manually stopping any environment from the UI
  Fix link to frontend in handbook
  Shorten CHANGELOG filename to avoid breaking ecryptfs users
  Replace 48976-rails5-invalid-single-table-inheritance-type-group-is-not-a-subclass-of-gitlab-backgroundmigration-fixcrossprojectlabellinks-namespace.yml
  Fix mountComponent helper path in docs
  Fix #48537 - Update avatar only via the projects API
  Add additional headline for Adding SSH keys to GitLab
  Request to be a proofreader.
  Fix specs
  Fix search bar text input alignment
  Fix API docs on unauthenticated projects return
  Adds with_projects optional parameter to /groups/:id API endpoint
  Docs: make it clear that you need a completely separate domain for Pages
  Document that we don't want to wait in tests
  Removes unused store in diffs mr refactor Removes double export for actions in diffs module in mr refactor
  Remove useless return
  Use latest gitlab-styles
  ...

This reverts merge request !20140

Discussions were being toggled by jquery DOM querying them and toggling
visibility but in vue, only the open discussions will be in the DOM
Fix includes:
 - Adds a getter to the store to get the expanded discussions
 - Adds an action to collapse a discussion
 - When the user clicks the button, all data needed is now accessible
   through a getter and we can dispatch an action to toggle the discussion
   within the state, instead of showing/hiding with jQuery
 - Removes hardcoded properties

Resolves #48237