Rewrite key management & signing

Extend compos_helper to support signing, use it from CompOS.

Expose the public key from the VM. Rename compos_verify_key to
compos_verify and get it to verify the signature against the current
instance's public key.

Also move DICE access to compos_key_main. There's no use having it in
the library - neither the tests nor compos_verify can use it - and it
complicates the build rules.

There's a lot more that can be deleted, but I'll do that in a
follow-up; this is big enough already.

Bug: 218494522
Test: atest CompOsSigningHostTest CompOsDenialHostTest
Change-Id: I2d71f68a595d5ddadb2e7b16937fa6855f5db0ab
diff --git a/compos/verify/Android.bp b/compos/verify/Android.bp
new file mode 100644
index 0000000..d6875d1
--- /dev/null
+++ b/compos/verify/Android.bp
@@ -0,0 +1,23 @@
+package {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+rust_binary {
+    name: "compos_verify",
+    srcs: ["verify.rs"],
+    edition: "2018",
+    rustlibs: [
+        "compos_aidl_interface-rust",
+        "libandroid_logger",
+        "libanyhow",
+        "libbinder_rs",
+        "libclap",
+        "libcompos_common",
+        "libcompos_verify_native_rust",
+        "liblog_rust",
+    ],
+    prefer_rlib: true,
+    apex_available: [
+        "com.android.compos",
+    ],
+}