Indent guides (#11503)

Builds on top of existing work from #2249, but here's a showcase:


https://github.com/zed-industries/zed/assets/53836821/4b346965-6654-496c-b379-75425d9b493f

TODO:
- [x] handle line wrapping
- [x] implement handling in multibuffer (crashes currently)
- [x] add configuration option
- [x] new theme properties? What colors to use?
- [x] Possibly support indents with different colors or background
colors
- [x] investigate edge cases (e.g. indent guides and folds continue on
empty lines even if the next indent is different)
- [x] add more tests (also test `find_active_indent_index`)
- [x] docs (will do in a follow up PR)
- [x] benchmark performance impact

Release Notes:

- Added indent guides
([#5373](https://github.com/zed-industries/zed/issues/5373))

---------

Co-authored-by: Nate Butler <1714999+iamnbutler@users.noreply.github.com>
Co-authored-by: Remco <djsmits12@gmail.com>

crates/theme/src/default_theme.rs

@@ -2,7 +2,7 @@ use std::sync::Arc;
 
 use gpui::WindowBackgroundAppearance;
 
-use crate::prelude::*;
+use crate::AccentColors;
 
 use crate::{
     default_color_scales,
@@ -23,21 +23,7 @@ fn zed_pro_daylight() -> Theme {
             status: StatusColors::light(),
             player: PlayerColors::light(),
             syntax: Arc::new(SyntaxTheme::default()),
-            accents: vec![
-                blue().light().step_9(),
-                orange().light().step_9(),
-                pink().light().step_9(),
-                lime().light().step_9(),
-                purple().light().step_9(),
-                amber().light().step_9(),
-                jade().light().step_9(),
-                tomato().light().step_9(),
-                cyan().light().step_9(),
-                gold().light().step_9(),
-                grass().light().step_9(),
-                indigo().light().step_9(),
-                iris().light().step_9(),
-            ],
+            accents: AccentColors::light(),
         },
     }
 }
@@ -54,21 +40,7 @@ pub(crate) fn zed_pro_moonlight() -> Theme {
             status: StatusColors::dark(),
             player: PlayerColors::dark(),
             syntax: Arc::new(SyntaxTheme::default()),
-            accents: vec![
-                blue().dark().step_9(),
-                orange().dark().step_9(),
-                pink().dark().step_9(),
-                lime().dark().step_9(),
-                purple().dark().step_9(),
-                amber().dark().step_9(),
-                jade().dark().step_9(),
-                tomato().dark().step_9(),
-                cyan().dark().step_9(),
-                gold().dark().step_9(),
-                grass().dark().step_9(),
-                indigo().dark().step_9(),
-                iris().dark().step_9(),
-            ],
+            accents: AccentColors::dark(),
         },
     }
 }