Wait for crosvm in a separate thread, and keep track of when it dies.

This lets us tell whether a VM is still running or has finished. Also
add callback so clients can get notified when crosvm dies.

Bug: 171277638
Test: Ran on VIM3L
Test: atest VirtualizationTestCases
Change-Id: I52c1625af45cfcfe7aa0be465ea08f427ec5bc43
diff --git a/virtmanager/Android.bp b/virtmanager/Android.bp
index 83ac3d6..f1971dc 100644
--- a/virtmanager/Android.bp
+++ b/virtmanager/Android.bp
@@ -14,6 +14,7 @@
         "liblog_rust",
         "libserde_json",
         "libserde",
+        "libshared_child",
         "libanyhow",
     ],
     apex_available: ["com.android.virt"],