Make the vm_payload API look more NDK-like

 - Give functions a `AVmPayload_` prefix followed by lower camel case
   name (hopefully better branding comes later, but this makes it easy
   to grep).
 - Let callers find out how big the attestation chain is.

Bug: 243514248
Test: atest MicrodroidTests ComposHostTestCases MicrodroidBenchmarks
Change-Id: I93c37787eae296d97a44cc369e8ea0c3c670c6cb
diff --git a/microdroid/vm_payload/src/lib.rs b/microdroid/vm_payload/src/lib.rs
index 74dd8f4..ca0c17b 100644
--- a/microdroid/vm_payload/src/lib.rs
+++ b/microdroid/vm_payload/src/lib.rs
@@ -17,6 +17,6 @@
 mod vm_service;
 
 pub use vm_service::{
-    get_dice_attestation_cdi, get_dice_attestation_chain, get_vm_instance_secret,
-    notify_payload_ready,
+    AVmPayload_getDiceAttestationCdi, AVmPayload_getDiceAttestationChain,
+    AVmPayload_getVmInstanceSecret, AVmPayload_notifyPayloadReady,
 };