Cleanup license metadata in external/rust/crates/data-encoding.

Add package and license module in Android.bp. File LICENSE is from upstream project, so use it in Android.bp.

Bug: 346390141
Test: CIs
Change-Id: I32af342a2c7be86ea4f6d0ab321d337e3be7375d
diff --git a/Android.bp b/Android.bp
index 7efbf95..6c1f3d9 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_data-encoding_license"],
+}
+
+license {
+    name: "external_rust_crates_data-encoding_license",
+    visibility: [":__subpackages__"],
+    license_kinds: [
+        "SPDX-license-identifier-MIT",
+    ],
+    license_text: [
+        "LICENSE",
+    ],
+}
+
 rust_library {
     name: "libdata_encoding",
     host_supported: true,