Upgrade idna to 0.5.0

This project was upgraded with external_updater.
Usage: tools/external_updater/updater.sh update external/rust/crates/idna
For more info, check https://cs.android.com/android/platform/superproject/+/main:tools/external_updater/README.md

Test: TreeHugger
Change-Id: I96d7c0adb55f3ef853a1acee00c92f64964c832a

src/lib.rs

diff --git a/src/lib.rs b/src/lib.rs
index 37d6387..92914f9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -31,11 +31,23 @@
 //! > This document specifies a mechanism
 //! > that minimizes the impact of this transition for client software,
 //! > allowing client software to access domains that are valid under either system.
+#![no_std]
+
+// For forwards compatibility
+#[cfg(feature = "std")]
+extern crate std;
+
+extern crate alloc;
+
+#[cfg(not(feature = "alloc"))]
+compile_error!("the `alloc` feature must be enabled");
 
 #[cfg(test)]
 #[macro_use]
 extern crate assert_matches;
 
+use alloc::string::String;
+
 pub mod punycode;
 mod uts46;