init: Add gentle_kill service property

If a service specifies gentle_kill, attempt to stop it will send SIGTERM
instead of SIGKILL. After 200ms, it will issue a SIGKILL.

Bug: 249043036
Test: atest CtsInitTestCases:init#GentleKill
      Added in next patch
Change-Id: Ieb0e4e24d31780aca1cf291f9d21d49cee181cf2
diff --git a/init/service.cpp b/init/service.cpp
index b9b3309..87d9c3a 100644
--- a/init/service.cpp
+++ b/init/service.cpp
@@ -26,6 +26,7 @@
 #include <sys/time.h>
 #include <termios.h>
 #include <unistd.h>
+#include <thread>
 
 #include <android-base/file.h>
 #include <android-base/logging.h>
@@ -887,6 +888,10 @@
     }
 
     if (pid_) {
+        if (flags_ & SVC_GENTLE_KILL) {
+            KillProcessGroup(SIGTERM);
+            if (!process_cgroup_empty()) std::this_thread::sleep_for(200ms);
+        }
         KillProcessGroup(SIGKILL);
         NotifyStateChange("stopping");
     } else {