Search improvement: Highlight all occurrences + show the occurrence count

Is your feature request related to a problem? Please describe.
Right now out of the box the search feature highlights one occurrence at a time. Sometimes it's useful to have a quick visual of all searched keywords in the buffer and an idea of how many occurrences were found.

Describe the solution you'd like
When a keyword is entered into the search bar:

• Highlight all occurrences in the current buffer in real time, preferably with separate color options (one option for all occurrences and another for current highlight). All of this updates as the buffer content changes.
• Show the number of occurrences in the search bar. Likewise, it updates as the buffer content changes.
• Bonus option: highlight occurrence positions in the scroll bar
• Another bonus option: allow RegEx search

The issue names no files, tests, or entry points. Start by locating the search bar and buffer-search implementation, then clarify whether the core scope includes occurrence highlighting and counts or also the bonus scrollbar markers and regex option. Done means the agreed search indicators update as the query and buffer content change.