adbd_auth: return auth id when requesting a prompt.

When multiple auth requests come in (e.g. if someone connects over TCP
and USB, or if we send a USB request, and then kill adb and try again),
we need to know the ID assigned to the request to disambiguate.

Bug: http://b/159061108
Test: manual
Change-Id: I68cf2335c5958decf29e58ed9132735577a7e074
diff --git a/libs/adbd_auth/adbd_auth.cpp b/libs/adbd_auth/adbd_auth.cpp
index 458d3fc..0e5d474 100644
--- a/libs/adbd_auth/adbd_auth.cpp
+++ b/libs/adbd_auth/adbd_auth.cpp
@@ -549,7 +549,12 @@
 
 void adbd_auth_prompt_user(AdbdAuthContext* ctx, const char* public_key, size_t len,
                            void* opaque) {
-    ctx->PromptUser(std::string_view(public_key, len), opaque);
+    adbd_auth_prompt_user_with_id(ctx, public_key, len, opaque);
+}
+
+uint64_t adbd_auth_prompt_user_with_id(AdbdAuthContext* ctx, const char* public_key, size_t len,
+                                       void* opaque) {
+    return ctx->PromptUser(std::string_view(public_key, len), opaque);
 }
 
 uint64_t adbd_auth_tls_device_connected(AdbdAuthContext* ctx,