Key blob protection using AEAD

Add BlobEncryptor, which can be used to write a secret (like our
private key) to an encrypted & authenticated blob and later retrieve
it.

Added the skeleton of code to make use of this, using the sealing CDI
as the input to the key derivation.

Bug: 214233409
Test: atest compsvc_device_tests
Change-Id: Iea7e82405072a31ae5f7ad64a9e894a970913219
diff --git a/TEST_MAPPING b/TEST_MAPPING
index c4ee878..6338c82 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -14,6 +14,9 @@
     },
     {
       "name": "art_standalone_dexpreopt_tests"
+    },
+    {
+      "name": "compsvc_device_tests"
     }
   ],
   "postsubmit": [