Let dumpstate call "cmd window trace save-for-bugreport"

This is a preparation to rework our previous CL [1], which enabled
"adb bugreport" to include winscope tracing files into bugreport.

In that CL, we used dumpsys with "--dump-priority CRITICAL" and
"--proto" options as a trigger to save winscope files for bugreport.

In this CL, we let dumpstate explicitly call the following shell command

  cmd window tracing save-for-bugreport

inspired by how Perfetto tracing is auto-included in bugreport [2].

  void Dumpstate::MaybeSnapshotSystemTrace() {
      ...

      int res = RunCommand(
          "SERIALIZE PERFETTO TRACE",
          {"perfetto", "--save-for-bugreport"},
          CommandOptions::WithTimeout(10)
              .DropRoot()
              .CloseAllFileDescriptorsOnExec()
              .Build());
      has_system_trace_ = res == 0;

      ...
  }

Note that with this CL winscope tracing files may contain more events
after saving WindowManager critical dump, it is supposed to be
ignorable as the command will be called immediately after taking
critical dumpsys.

On branches where WindowManagerService does not support the above
command, this CL will have no-op except for the following one-line log
will be seen in logcat.

    02-20 00:56:30.754  root  5325  5325 E dumpstate:        \
        *** command 'cmd window tracing save-for-bugreport'  \
        failed: exit code 255

To summarize, WinScope logs continue to be dumped under
  "/data/misc/wmtrace/"
in the bugreport, and size impact also remains to be the same.
  wm_trace.pb: At most 2MB by default
  wm_log.pb :  At most 1MB by default

 [1]: I102bc4afab5efff361633d75c09af1df4a11812e
      9e2604688d4c64ea95128f9d8b3b08da508532dd

Bug: 177462676
Test: Manually done as follows.
  1. adb logcat -d -s WindowTracing:*
       Make sure wintrace is not yet running
  2. adb logcat -d -s WindowTracing:*
       Make sure there is no additional message
  3. adb shell cmd window tracing start
  4. adb logcat -d -s WindowTracing:*
       Make sure wintrace is running
  5. adb bugreport bugreport.zip
  6. adb logcat -d -s WindowTracing:*
       Make sure wintrace stopped then restarted if
       WMS supports "tracing save-for-bugreport".
  7. unzip -v bugreport.zip | grep wm_trace.pb
       Make sure "wm_trace.pb" is included if
       WMS supports "tracing save-for-bugreport"
Change-Id: I8be9dee9aa36c2b085596d58e418f8613d874500