Fix the following style-lint errors and warnings for `app/assets/stylesheets/framework/selects.scss`

Problem

Fix the following style-lint errors and warnings for app/assets/stylesheets/framework/selects.scss

   2:1  ⚠  ".select2-container" has the same properties as our BS4 utility class ".w-100 (834:1)" so please use that instead.                                                                            stylelint-gitlab/utility-classes
  30:7  ⚠  Expected ".select2-container .select2-choice .select2-arrow b" to have no more than 3 compound selectors                                                                                      selector-max-compound-selectors
  30:7  ⚠  Expected ".select2-container.select2-drop-above .select2-choice .select2-arrow b" to have no more than 3 compound selectors                                                                   selector-max-compound-selectors
  62:5  ⚠  "~ .invalid-feedback" and "&.input-md,   &.input-lg (/Users/filipalacerda/Documents/git/gitlab-development-kit/gitlab/app/assets/stylesheets/framework/selects.scss -5:3)" have the same      stylelint-gitlab/duplicate-selectors
           properties.
 120:5  ⚠  Expected ".select2-container-multi .select2-choices .select2-search-field input" to have no more than 3 compound selectors                                                                    selector-max-compound-selectors
 137:7  ⚠  Expected ".select2-container-multi .select2-choices .select2-search-choice .select2-search-choice-close" to have no more than 3 compound selectors                                            selector-max-compound-selectors
 162:3  ⚠  ".select2-drop-auto-width &" and ".select2-search (/Users/filipalacerda/Documents/git/gitlab-development-kit/gitlab/app/assets/stylesheets/framework/selects.scss -159:1)" have the same      stylelint-gitlab/duplicate-selectors
           properties.
 268:3  ⚠  ".project-name" and ".group-name (/Users/filipalacerda/Documents/git/gitlab-development-kit/gitlab/app/assets/stylesheets/framework/selects.scss -258:3)" have the same properties.           stylelint-gitlab/duplicate-selectors
 272:3  ⚠  ".project-path" and ".group-path (/Users/filipalacerda/Documents/git/gitlab-development-kit/gitlab/app/assets/stylesheets/framework/selects.scss -262:3)" have the same properties.           stylelint-gitlab/duplicate-selectors
 282:3  ⚠  ".user-image" and ".group-image (/Users/filipalacerda/Documents/git/gitlab-development-kit/gitlab/app/assets/stylesheets/framework/selects.scss -254:3)" have the same properties.            stylelint-gitlab/duplicate-selectors

What to do

  1. If possible, replace the CSS class with a utility one, check common.scss and https://getbootstrap.com/docs/4.3/utilities/ for existing ones
  2. Double check if all the warning have been fixed by running yarn run stylelint-file app/assets/stylesheets/framework/selects.scss
  3. In the MR, add screenshots of the affected areas before and after the changes, check the first MR as a guideline
  4. If there are a lot of changes, we recommend to break them into smaller MRs
  5. Double check the usage of each changed class both in CE and EE
  6. EE changes should either be backported into CE or moved into ee/ folder. You can read more about how to handle EE code here
  7. Label the MR with CSS cleanup