FIX: Improve quick search speed and result highlights (PR #14610)

Two small fixes:

  • when in a topic and searching for topic:ID keyword, keyword was not being highlighted
  • since full topic/post searches now require explicit action (Enter or click), we no longer need to debounce these calls


Would this regex be better if it looked for a word boundary \b before “topic”?

Yeah, that would be safer. Will add.