arcvm: Merge platform2's arcvm_launch.cc back into Chromium

See go/arcvm-lifetime-v2 for more context. The key differences
between the original code in arcvm_launch.cc and this are:

* This CL uses DCHECK and variants rather than CHECK.
* This CL uses VLOG and variants rather than LOG(INFO).
* This CL uses base's string/number conversion functions rather
  than std's.
* This CL async calls to Concierge since sync ones are not usable
  here.
* The crossystem wrapper function is reimplemented.
* The unittest (which was removed in 46d42eef) is restored with some
  additional tests for verifying crosvm and Concierge crash handling
  code.

BUG=b:142144019
TEST=ran the unit tests + arc.Boot

Change-Id: Iba3d37aaf1527ffc76165cd93c0e121d1e226308
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1848772Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704789}

components/arc/BUILD.gn

@@ -361,6 +361,7 @@ source_set("unit_tests") {
     "session/arc_data_remover_unittest.cc",
     "session/arc_session_impl_unittest.cc",
     "session/arc_session_runner_unittest.cc",
+    "session/arc_vm_client_adapter_unittest.cc",
     "timer/arc_timer_bridge_unittest.cc",
     "wake_lock/arc_wake_lock_bridge_unittest.cc",
   ]