[cbor] Use libcoset/libciborium to convert ed25519 pub key to cbor

This replaces the manual serialization and makes the code easier
to read and maintain.

The test diced_open_dice_cbor_test ensures that the result is
exactly the same as before.

Test: atest diced_open_dice_cbor_test
Change-Id: Ice6ed3f71875c52a11e1fe4c36d5ff0d8ab9ae6d
diff --git a/diced/Android.bp b/diced/Android.bp
index 6bd7c06..22e069a 100644
--- a/diced/Android.bp
+++ b/diced/Android.bp
@@ -51,6 +51,8 @@
 
     rustlibs: [
         "libanyhow",
+        "libciborium",
+        "libcoset",
         "libdiced_open_dice",
         "libdiced_utils",
     ],
@@ -64,6 +66,8 @@
     auto_gen_config: true,
     rustlibs: [
         "libanyhow",
+        "libciborium",
+        "libcoset",
         "libdiced_open_dice",
         "libdiced_utils",
     ],