Tidy up the context switcher changes

Proposal

See #409522 (closed) for original context

• Remove the hr line from above pinned
• Add oxford comma to global search modal
• Rebalance vertical padding of Search button (see !127935 (comment 1524988851))
• Adjust spacing and alignment in user-bar → !130629 (merged)
• Add space between active indicator and avatar (see !129843 (comment 1532538817)): !131798 (merged)
• Update context titles to correspond with themes (see !129843 (comment 1532554831)): !131798 (merged)
• Remove unused context switcher code: !129935 (merged)