libvm_payload as a cc_library

Define a symbole file for libvm_payload, and request stubs. Make sure
the clients build against the stubs.

Mark the implementation as not required, to prevent the missing
dependencies check triggering; it is actually present at runtime
inside Microdroid.

Bug: 243512108
Bug: 255920361
Test: atest MicrodroidTests
Test: composd-cmd test-compile
Change-Id: I78c33b6fba706fd0e52435ac13d02a25171862f1
diff --git a/vm_payload/libvm_payload.map.txt b/vm_payload/libvm_payload.map.txt
new file mode 100644
index 0000000..a2402d1
--- /dev/null
+++ b/vm_payload/libvm_payload.map.txt
@@ -0,0 +1,12 @@
+LIBVM_PAYLOAD {
+  global:
+    AVmPayload_notifyPayloadReady;       # systemapi
+    AVmPayload_runVsockRpcServer;        # systemapi
+    AVmPayload_getVmInstanceSecret;      # systemapi
+    AVmPayload_getDiceAttestationChain;  # systemapi
+    AVmPayload_getDiceAttestationCdi;    # systemapi
+    AVmPayload_getApkContentsPath;       # systemapi
+    AVmPayload_getEncryptedStoragePath;  # systemapi
+  local:
+    *;
+};