Project panel horizontal scrollbar (#18513)

<img width="389" alt="image"
src="https://github.com/user-attachments/assets/c6718c6e-0fe1-40ed-b3db-7d576c4d98c8">


https://github.com/user-attachments/assets/734f1f52-70d9-4308-b1fc-36c7cfd4dd76

Closes https://github.com/zed-industries/zed/issues/7001
Closes https://github.com/zed-industries/zed/issues/4427
Part of https://github.com/zed-industries/zed/issues/15324
Part of https://github.com/zed-industries/zed/issues/14551

* Adjusts a `UniformList` to have a horizontal sizing behavior: the old
mode forced all items to have the size of the list exactly.
A new mode (with corresponding `ListItems` having `overflow_x` enabled)
lays out the uniform list elements with width of its widest element,
setting the same width to the list itself too.

* Using the new behavior, adds a new scrollbar into the project panel
and enhances its file name editor to scroll it during editing of long
file names

* Also restyles the scrollbar a bit, making it narrower and removing its
background

* Changes the project_panel.scrollbar.show settings to accept `null` and
be `null` by default, to inherit `editor`'s scrollbar settings. All
editor scrollbar settings are supported now.

Release Notes:

- Added a horizontal scrollbar to project panel
([#7001](https://github.com/zed-industries/zed/issues/7001))
([#4427](https://github.com/zed-industries/zed/issues/4427))

---------

Co-authored-by: Piotr Osiewicz <piotr@zed.dev>

crates/language/src/language_settings.rs

@@ -381,7 +381,7 @@ pub struct FeaturesContent {
 pub enum SoftWrap {
     /// Prefer a single line generally, unless an overly long line is encountered.
     None,
-    /// Deprecated: use None instead. Left to avoid breakin existing users' configs.
+    /// Deprecated: use None instead. Left to avoid breaking existing users' configs.
     /// Prefer a single line generally, unless an overly long line is encountered.
     PreferLine,
     /// Soft wrap lines that exceed the editor width.