chore: Prepare for Rust edition bump to 2024 (without autofix) (#27791)

Successor to #27779 - in this PR I've applied changes manually, without
futzing with if let lifetimes at all.

Release Notes:

- N/A

crates/extension_api/src/extension_api.rs

@@ -185,7 +185,7 @@ pub trait Extension: Send + Sync {
 #[macro_export]
 macro_rules! register_extension {
     ($extension_type:ty) => {
-        #[export_name = "init-extension"]
+        #[unsafe(export_name = "init-extension")]
         pub extern "C" fn __init_extension() {
             std::env::set_current_dir(std::env::var("PWD").unwrap()).unwrap();
             zed_extension_api::register_extension(|| {