Cleanup license metadata in external/rust/crates/annotate-snippets.

Add package and license module in Android.bp. Symlink file LICENSE is added in Android codebase and points to LICENSE-APACHE, so use it in Android.bp.

Bug: 346390141
Test: CIs

Change-Id: I54789ab6952fecb441f722e43369893402020c5f
diff --git a/Android.bp b/Android.bp
index 69902b5..70a00b5 100644
--- a/Android.bp
+++ b/Android.bp
@@ -3,6 +3,21 @@
 // because the changes will be overridden on upgrade.
 // Content before the first "rust_*" or "genrule" module is preserved.
 
+package {
+    default_applicable_licenses: ["external_rust_crates_annotate-snippets_license"],
+}
+
+license {
+    name: "external_rust_crates_annotate-snippets_license",
+    visibility: [":__subpackages__"],
+    license_kinds: [
+        "SPDX-license-identifier-Apache-2.0",
+    ],
+    license_text: [
+        "LICENSE",
+    ],
+}
+
 rust_library_host {
     name: "libannotate_snippets",
     crate_name: "annotate_snippets",