Search: highlight all matches at once, with total count (N of M) and scrollbar position markers

[kjk]

Split out from the (now-closed) search umbrella #154. Closely related to the closed #1765 ("Highlight and number matching instances in search results").

Request: make in-document search behave like Chrome/Firefox, where all occurrences are visible at once, not just the current one. Concretely:

• highlight all matches of the current search term simultaneously (the current match emphasized differently from the rest)
• show a total count and current position, e.g. 5 / 117, in the find UI
• put small markers on the scrollbar indicating where matches are in the document
• (from the original Find / Search features #154 list) allow dismissing an individual highlight (click to de-highlight) and/or keeping highlights persistent

These are grouped because they're one coherent feature (the "search results overview" UX) and would be implemented together. They could complement, or be folded into, the Find All panel (#5691).

[r5to]

If it is not a bad idea, i would like to call some glitches and requests here...

1. resizing search window makes refresh glitch on page number:

2. there is lag on search, when results need to scroll search window on the first time scroll. When you make inverse search with Shift+F3 and again with F3 - lag is gone. You need to search with F3 by holding it. When you use mouse to scroll up and select first result and try to search with F3 lag is here again.

3. there is not possible to loop search in search window like without it, in standard simple search (maybe it is not needed (??), but just im telling it works different)

4. would be nice to have old behavior when first result is marked again, like in 3.6 version (sound + highlight):

5. when you have small width window, then search dialog looks like this:

[kjk]

@r5to thanks for testing, good suggestions.

I've implemented most of them.

For future suggestions, please open new issues to make it easier to track the status of fixing them.

[kjk]

Gonna skip scollbar markers and dismissing highlight