Use mimalloc as default allocator (#7140)

From https://github.com/microsoft/mimalloc:
> In our benchmarks (see
[below](https://github.com/microsoft/mimalloc#performance)), mimalloc
outperforms other leading allocators (jemalloc, tcmalloc, Hoard, etc),
and often uses less memory. A nice property is that it does consistently
well over a wide range of benchmarks. There is also good huge OS page
support for larger server programs.


Release Notes:

- Changed default allocator to mimalloc.

crates/zed/src/main.rs

@@ -18,6 +18,7 @@ use language::LanguageRegistry;
 use log::LevelFilter;
 
 use assets::Assets;
+use mimalloc::MiMalloc;
 use node_runtime::RealNodeRuntime;
 use parking_lot::Mutex;
 use release_channel::{parse_zed_link, AppCommitSha, ReleaseChannel, RELEASE_CHANNEL};
@@ -57,6 +58,9 @@ use zed::{
     OpenRequest,
 };
 
+#[global_allocator]
+static GLOBAL: MiMalloc = MiMalloc;
+
 fn main() {
     menu::init();
     zed_actions::init();