linux: Fix wrong cursor theme for arrow cursor style (#22276)

Closes #22264

On Linux, the arrow cursor style currently used by Zed is `arrow`.
However, this style might not be available in most themes, causing the
cursor to fall back to system default theme. Note cursor style are
platform (X11 and Wayland) agnostic.

Most themes use `left_ptr` as their arrow cursor style instead of
`arrow`. In some cases, `left_ptr` and `arrow` are symlinks pointing to
the `default` style, but the `default` style is not guaranteed to be
available across all themes.

After inspecting the available cursor themes on popular desktop
environments, changing the default from `arrow` to `left_ptr` seems to
be available in all of them. `left_ptr` as default cursor style is also
mentioned in [Arch Wiki: Cursor
themes](https://wiki.archlinux.org/title/Cursor_themes#Change_X_shaped_default_cursor).

KDE:
```sh
tims@lemon /u/s/icons> find . -name "arrow"
./Breeze_Snow/cursors/arrow
./breeze_cursors/cursors/arrow
./Adwaita/cursors/arrow

tims@lemon /u/s/icons> find . -name "default"
./default
./Breeze_Snow/cursors/default
./breeze_cursors/cursors/default
./Adwaita/cursors/default

tims@lemon /u/s/icons> find . -name "left_ptr"
./Oxygen_White/cursors/left_ptr
./KDE_Classic/cursors/left_ptr
./Oxygen_Yellow/cursors/left_ptr
./Oxygen_Blue/cursors/left_ptr
./Oxygen_Black/cursors/left_ptr
./Breeze_Snow/cursors/left_ptr
./breeze_cursors/cursors/left_ptr
./Adwaita/cursors/left_ptr
./Oxygen_Zion/cursors/left_ptr

```

Gnome:
```sh
tims@orange:/usr/share/icons$ find . -name "arrow"
./DMZ-Black/cursors/arrow
./Adwaita/cursors/arrow
./redglass/cursors/arrow
./whiteglass/cursors/arrow
./handhelds/cursors/arrow
./Yaru/cursors/arrow
./DMZ-White/cursors/arrow

tims@orange:/usr/share/icons$ find . -name "default"
./Adwaita/cursors/default
./default
./Yaru/cursors/default

tims@orange:/usr/share/icons$ find . -name "left_ptr"
./DMZ-Black/cursors/left_ptr
./Adwaita/cursors/left_ptr
./redglass/cursors/left_ptr
./whiteglass/cursors/left_ptr
./handhelds/cursors/left_ptr
./Yaru/cursors/left_ptr
./DMZ-White/cursors/left_ptr
```

My theme is set to Oxygen Yellow here.

Before:
<img
src="https://github.com/user-attachments/assets/7485f1e7-5936-45b4-96bd-399525bad95d"
alt="before" width="450px" />

After:
<img
src="https://github.com/user-attachments/assets/56090735-6a1f-4652-ad3e-075ff4c3f9ab"
alt="after" width="450px" />


Release Notes:

- Fixed wrong cursor theme for arrow cursor style on Linux.

crates/gpui/src/platform/linux/platform.rs

@@ -651,7 +651,7 @@ impl CursorStyle {
         // and https://github.com/KDE/breeze (KDE). Both of them seem to be also derived from
         // Web CSS cursor names: https://developer.mozilla.org/en-US/docs/Web/CSS/cursor#values
         match self {
-            CursorStyle::Arrow => "arrow",
+            CursorStyle::Arrow => "left_ptr",
             CursorStyle::IBeam => "text",
             CursorStyle::Crosshair => "crosshair",
             CursorStyle::ClosedHand => "grabbing",