editor: Add horizontal scrollbar (#19495)

![editor_scrollbars](https://github.com/user-attachments/assets/76c26776-8fe4-47f8-9c79-9add7d7d2151)

Closes #4427 

Release Notes:

- Added a horizontal scrollbar to the editor panel
- Added `axis` option to `scrollbar` in the Zed configuration, which can
forcefully disable either the horizontal or vertical scrollbar
- Added `horizontal_scroll_margin` equivalent to
`vertical_scroll_margin` in the Zed configuration

Rough Edges:

This feature seems mostly stable from my testing. I've been using a
development build for about a week with no issues. Any feedback would be
appreciated. There are a few things to note as well:

1. Scrolling to the lower right occasionally causes scrollbar clipping
on my end, but it isn't consistent and it isn't major. Some more testing
would definitely be a good idea. [FIXED]
2. Documentation may need to be modified
3. I added an `AxisPair` type to the `editor` crate to manage values
that have a horizontal and vertical variant. I'm not sure if that's the
optimal way to do it, but I didn't see a good alternative. The `Point`
type would technically work, but it may cause confusion.

---------

Co-authored-by: Piotr Osiewicz <24362066+osiewicz@users.noreply.github.com>

crates/search/src/project_search.rs

@@ -5,18 +5,16 @@ use crate::{
 };
 use collections::{HashMap, HashSet};
 use editor::{
-    actions::SelectAll,
-    items::active_match_index,
-    scroll::{Autoscroll, Axis},
-    Anchor, Editor, EditorElement, EditorEvent, EditorSettings, EditorStyle, MultiBuffer,
-    MAX_TAB_TITLE_LEN,
+    actions::SelectAll, items::active_match_index, scroll::Autoscroll, Anchor, Editor,
+    EditorElement, EditorEvent, EditorSettings, EditorStyle, MultiBuffer, MAX_TAB_TITLE_LEN,
 };
 use futures::StreamExt;
 use gpui::{
-    actions, div, Action, AnyElement, AnyView, AppContext, Context as _, EntityId, EventEmitter,
-    FocusHandle, FocusableView, Global, Hsla, InteractiveElement, IntoElement, KeyContext, Model,
-    ModelContext, ParentElement, Point, Render, SharedString, Styled, Subscription, Task,
-    TextStyle, UpdateGlobal, View, ViewContext, VisualContext, WeakModel, WeakView, WindowContext,
+    actions, div, Action, AnyElement, AnyView, AppContext, Axis, Context as _, EntityId,
+    EventEmitter, FocusHandle, FocusableView, Global, Hsla, InteractiveElement, IntoElement,
+    KeyContext, Model, ModelContext, ParentElement, Point, Render, SharedString, Styled,
+    Subscription, Task, TextStyle, UpdateGlobal, View, ViewContext, VisualContext, WeakModel,
+    WeakView, WindowContext,
 };
 use language::Buffer;
 use menu::Confirm;