windows: Remove null terminator from keyboard ID (#41785)

Closes #41486, closes #35862 

It is unnecessary, and it broke the `uses_altgr` function.

Also add Slovenian layout as using AltGr.

This should fix:
-
https://github.com/zed-industries/zed/pull/40536#issuecomment-3477121224
- https://github.com/zed-industries/zed/issues/41486
- https://github.com/zed-industries/zed/issues/35862

As the current strategy relies on manually adding layouts that have
AltGr, it's brittle and not very elegant. It also has other issues (it
requests the current layout on every kesytroke and mouse movement).

**A potentially better and more comprehensive solution is at
https://github.com/zed-industries/zed/pull/41259**
This is just to fix the immediate issues while that gets reviewed.

Release Notes:

- windows: Fix AltGr handling on non-US layouts again.

crates/gpui/src/platform/windows/keyboard.rs

@@ -9,7 +9,6 @@ use windows::Win32::UI::{
     },
     WindowsAndMessaging::KL_NAMELENGTH,
 };
-use windows_core::HSTRING;
 
 use crate::{
     KeybindingKeystroke, Keystroke, Modifiers, PlatformKeyboardLayout, PlatformKeyboardMapper,
@@ -93,14 +92,13 @@ impl PlatformKeyboardMapper for WindowsKeyboardMapper {
 
 impl WindowsKeyboardLayout {
     pub(crate) fn new() -> Result<Self> {
-        let mut buffer = [0u16; KL_NAMELENGTH as usize];
+        let mut buffer = [0u16; KL_NAMELENGTH as usize]; // KL_NAMELENGTH includes the null terminator
         unsafe { GetKeyboardLayoutNameW(&mut buffer)? };
-        let id = HSTRING::from_wide(&buffer).to_string();
+        let id = String::from_utf16_lossy(&buffer[..buffer.len() - 1]); // Remove the null terminator
         let entry = windows_registry::LOCAL_MACHINE.open(format!(
-            "System\\CurrentControlSet\\Control\\Keyboard Layouts\\{}",
-            id
+            "System\\CurrentControlSet\\Control\\Keyboard Layouts\\{id}"
         ))?;
-        let name = entry.get_hstring("Layout Text")?.to_string();
+        let name = entry.get_string("Layout Text")?;
         Ok(Self { id, name })
     }
 
@@ -135,6 +133,7 @@ impl WindowsKeyboardLayout {
                 b"0405" | // Czech
                 b"040E" | // Hungarian
                 b"0424" | // Slovenian
+                b"041A" | // Croatian
                 b"041B" | // Slovak
                 b"0418" // Romanian
             )