Implement JVMTI can_signal_thread capability.

Implements the JVMTI can_signal_thread capability and all associated
methods and behaviors. This includes both the StopThread and
InterruptThread functions.

This CL contains the tests for the previous CL.

Test: ./test.py --host -j50
Test: stress --cpu 59 && while ./test/run-test --host 1934; do; done

Bug: 62821960
Bug: 34415266
Change-Id: I7b6fc37da0d2673caa993e486f078cf129d74c0f
diff --git a/openjdkjvmti/ti_thread.h b/openjdkjvmti/ti_thread.h
index ceebff6..09b4cab 100644
--- a/openjdkjvmti/ti_thread.h
+++ b/openjdkjvmti/ti_thread.h
@@ -93,6 +93,9 @@
                                      const jthread* threads,
                                      jvmtiError* results);
 
+  static jvmtiError StopThread(jvmtiEnv* env, jthread thr, jobject exception);
+  static jvmtiError InterruptThread(jvmtiEnv* env, jthread thr);
+
   // Returns true if we decoded the thread and it is alive, false otherwise with an appropriate
   // error placed into 'err'. A thread is alive if it has had it's 'start' function called and has
   // (or at least could have) executed managed code and has not yet returned past it's first managed