editor: Add search highlighting for active elements

[DarkMatter-999]

Closes #28617

Release Notes:

• Improved search text highlighting, the currently selected search result is highlighted in a different shade improving visibility.

Before

After

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[DarkMatter-999]

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[smitbarmase]

Looks good, just left few notes.

[DarkMatter-999]

@smitbarmase, made the required changes, please re-review.

                "search.match_background": "#00FF007F",
                "search.active_match_background": "#FF00007F",

[smitbarmase]

We are almost there.

1. I think it would be great to actually define sensible colors for at least the theme we support out of the box. You can find them in assets/themes. It should be distinct enough or straight up complementary, since even with two matches you should be able to identify which one is active.

Zed with this PR:

VSCode:

Sublime:

2. We also don't want to break any theme, since after this change, active highlight might start to look different for different themes. I think we should fallback to search_match_background if search_active_match_background is not specified. Right now, fallback works only if both search_match_background and search_active_match_background aren't specified.

[smitbarmase]

I think it's alright to not have these comments, since variable naming is apparent.

[DarkMatter-999]

Hey @smitbarmase I've updated the default themes and added backward compatibility for other themes as fallback to search_match_background. Please review.

[smitbarmase]

Hey @DarkMatter-999, after digging deeper into this, I found a major issue with the approach. Using a separate highlight key for the active match might not be the best idea because:

1. If you need to query all match highlights, it becomes harder to merge the active match with the non-active ones. For example, get_matches expects everything in sorted order. With the current state of this PR, the Outline Panel breaks because it expects a full sorted list. We’d have to binary-search the correct position for the active match and then return it, which is unnecessary extra work.

2. Similarly, in update_matches, the check existing_range != Some(matches) will always fail, since it’s comparing all matches with only the non-active ones. We’d have to manually construct the correct ordered list there too. If you add a dbg in the current version, you’ll notice how often this method runs, because that check always fails and triggers MatchesInvalidated.

I started from scratch and after experimenting, I ended up with this PR: #44098. Thanks to you for the theme changes, I cherry-picked them as is. Thanks for your contribution! I’m closing this in favor of that PR.