Bypass detection by skipping imported keys (#12)

In patch mode, a key's origin provides a robust way to avoid modifying
user-imported keys, which is a well-known detection vector. This commit
implements a new strategy to check the `KeyOrigin` tag from the key's
metadata. If a key is marked as `IMPORTED` or `SECURELY_IMPORTED`, the
patching process is now skipped entirely.

This new origin-based check is more reliable and cleaner than the
previous fingerprinting implementation, which has been removed.

Additionally, this commit acknowledges a remaining detection vector in
patch mode: when an `attestationKey` is used, a key must be generated.
Purely software-generated keys are detectable. To address this in the
future, the full software "generate mode" must be implemented even for
devices without a broken TEE. The old key generation logic has been
stubbed with a TODO in preparation for this redesign.

stub/src/main/java/android/hardware/security/keymint/KeyOrigin.java

@@ -0,0 +1,9 @@
+package android.hardware.security.keymint;
+
+public @interface KeyOrigin {
+    int GENERATED = 0;
+    int DERIVED = 1;
+    int IMPORTED = 2;
+    int RESERVED = 3;
+    int SECURELY_IMPORTED = 4;
+}