Enable exporting of tombstones out of guest VMs

Microdroid init will start the tombstone_transmit service which will
connect to a server (thread of virtualization service).

virtualizationservice listens for incoming connections from guests VMs.
The client (tombstone_transmit in  guest) sends each tombstone file
content through a separate stream.

For each received connection, handle_tombstone would send a connect
request to tombstoned(via libtombstoned_client_rust), which provide a
file  to write the content in (actually managed by the client libary).
Once write is complete notify_completion() would send completion
notification to tombstoned (which then will close the file and rename it).

Test: atest MicrodroidHostTestCases and/or crash a process in microdroid, take and check bugreport
Bug: 202153827

Change-Id: Ifcaa5da968ef39fdd05612d3e0baca4fd1c5eaf1
diff --git a/microdroid/Android.bp b/microdroid/Android.bp
index 4901351..77c0b68 100644
--- a/microdroid/Android.bp
+++ b/microdroid/Android.bp
@@ -77,6 +77,7 @@
         "linkerconfig",
         "servicemanager.microdroid",
         "tombstoned",
+        "tombstone_transmit.microdroid",
         "cgroups.json",
         "public.libraries.android.txt",