message: Restore `center-reactions-popup` feature
diff: -/* Hide reaction popover text */
  -.js-add-reaction-popover :is(.color-text-secondary, .color-fg-muted),
  -.js-add-reaction-popover .dropdown-divider {
  - display: none;
  -}
  -
  -/* Center reactions popup and its triangle */
  -.add-reaction-popover,
  -.add-reaction-popover::before,
  -.add-reaction-popover::after {
  - right: auto !important;
  +.dropdown-menu-reactions.dropdown-menu-reactions { /* Double selector to override .d-flex on Chrome */
  + top: 100% !important;
  left: 50% !important;
  + right: auto !important;
  transform: translate(-50%) !important;
  -}
  -
  -.add-reaction-popover {
  - animation-name: rgh-scale-in-centered !important;
  -}
  -
  -@keyframes rgh-scale-in-centered {
  - 0% {
  - transform: translate(-50%) scale(0.5);
  - opacity: 0%;
  - }
  -
  - 100% {
  - transform: translate(-50%);
  - }
  -}
  -
  -/*
  -Undo reactions popup centering in split file view on the right.
  -The popup is clipped on the right otherwise.
  -The selector considers
  -- Unified view (skipped)
  -- Split view with comment on the left only (skipped)
  -- Split view with comment on the right only
  -- Split view with comments on the left and right
  -*/
  -td.js-line-comments:last-child .timeline-comment-actions .add-reaction-popover {
  - left: -15px !important;
  -}
  -
  -td.js-line-comments:last-child .timeline-comment-actions .add-reaction-popover::before,
  -td.js-line-comments:last-child .timeline-comment-actions .add-reaction-popover::after {
  - left: 140px !important;
  -}
  -
  -/* Never show loading spinner for reactions */
  -.js-reaction-popover-container .reaction-popover-form .loading-spinner {
  - display: none !important;
  -}
  -
  -/* Keep colored button when reaction popup is open */
  -.dropdown-details[open] .timeline-comment-action {
  - opacity: 100%;
  - color: var(--color-mktg-btn-bg, #4078c0);
  + display: grid !important;
  + grid-template: auto / repeat(4, auto); /* Restore two-line layout */
  }
  