editor: Add minimap (#26893)

## Overview

This PR adds the minimap feature to the Zed editor, closely following
the [design from Visual Studio
Code](https://code.visualstudio.com/docs/getstarted/userinterface#_minimap).
When configured, a second instance of the editor will appear to the left
of the scrollbar. This instance is not interactive and it has a slimmed
down set of annotations, but it is otherwise just a zoomed-out version
of the main editor instance. A thumb shows the line boundaries of the
main viewport, as well as the progress through the document. Clicking on
a section of code in the minimap will jump the editor to that code.
Dragging the thumb will act like the scrollbar, moving sequentially
through the document.

![screenshot of Zed with three editors open and the minimap enabled,
showing the
slider](https://github.com/user-attachments/assets/4178d23a-a5ea-4e38-b871-06dd2a8f9560)

## New settings

This adds a `minimap` section to the editor settings with the following
keys:

### `show`

When to show the minimap in the editor.
This setting can take three values:
1. Show the minimap if the editor's scrollbar is visible: `"auto"`
2. Always show the minimap: `"always"`
3. Never show the minimap: `"never"` (default)

### `thumb`

When to show the minimap thumb.
This setting can take two values:
1. Show the minimap thumb if the mouse is over the minimap: `"hover"`
2. Always show the minimap thumb: `"always"` (default)

### `width`

The width of the minimap in pixels.

Default: `100`

### `font_size`

The font size of the minimap in pixels.

Default: `2`

## Providing feedback

In order to keep the PR focused on development updates, please use the
discussion thread for feature suggestions and usability feedback: #26894


## Features left to add

- [x] fix scrolling performance
- [x] user settings for enable/disable, width, text size, etc.
- [x] show overview of visible lines in minimap
- [x] clicking on minimap should navigate to the corresponding section
of code
- ~[ ] more prominent highlighting in the minimap editor~
- ~[ ] override scrollbar auto setting to always when minimap is set to
always show~

Release Notes:

- Added minimap for high-level overview and quick navigation of editor
contents.

---------

Co-authored-by: MrSubidubi <dev@bahn.sh>
Co-authored-by: Kirill Bulatov <kirill@zed.dev>

crates/assistant_context_editor/src/context_editor.rs

@@ -242,9 +242,9 @@ impl ContextEditor {
         let editor = cx.new(|cx| {
             let mut editor =
                 Editor::for_buffer(context.read(cx).buffer().clone(), None, window, cx);
+            editor.disable_scrollbars_and_minimap(cx);
             editor.set_soft_wrap_mode(SoftWrap::EditorWidth, cx);
             editor.set_show_line_numbers(false, cx);
-            editor.set_show_scrollbars(false, cx);
             editor.set_show_git_diff_gutter(false, cx);
             editor.set_show_code_actions(false, cx);
             editor.set_show_runnables(false, cx);
@@ -942,7 +942,7 @@ impl ContextEditor {
                     let patch_range = range.clone();
                     move |cx: &mut BlockContext| {
                         let max_width = cx.max_width;
-                        let gutter_width = cx.gutter_dimensions.full_width();
+                        let gutter_width = cx.margins.gutter.full_width();
                         let block_id = cx.block_id;
                         let selected = cx.selected;
                         let window = &mut cx.window;
@@ -1488,7 +1488,7 @@ impl ContextEditor {
 
                         h_flex()
                             .id(("message_header", message_id.as_u64()))
-                            .pl(cx.gutter_dimensions.full_width())
+                            .pl(cx.margins.gutter.full_width())
                             .h_11()
                             .w_full()
                             .relative()
@@ -1583,6 +1583,7 @@ impl ContextEditor {
                 ),
                 priority: usize::MAX,
                 render: render_block(MessageMetadata::from(message)),
+                render_in_minimap: false,
             };
             let mut new_blocks = vec![];
             let mut block_index_to_message = vec![];
@@ -2157,12 +2158,12 @@ impl ContextEditor {
                             let image_size = size_for_image(
                                 &image,
                                 size(
-                                    cx.max_width - cx.gutter_dimensions.full_width(),
+                                    cx.max_width - cx.margins.gutter.full_width(),
                                     MAX_HEIGHT_IN_LINES as f32 * cx.line_height,
                                 ),
                             );
                             h_flex()
-                                .pl(cx.gutter_dimensions.full_width())
+                                .pl(cx.margins.gutter.full_width())
                                 .child(
                                     img(image.clone())
                                         .object_fit(gpui::ObjectFit::ScaleDown)
@@ -2172,6 +2173,7 @@ impl ContextEditor {
                                 .into_any_element()
                         }),
                         priority: 0,
+                        render_in_minimap: false,
                     })
                 })
                 .collect::<Vec<_>>();