[docs] Add Missing JNI docs from C++ (NFC) (#6139)

wpiutil/src/main/java/edu/wpi/first/util/WPIUtilJNI.java

@@ -82,18 +82,67 @@ public class WPIUtilJNI {
 
   public static native long getSystemTime();
 
+  /**
+   * Creates an event. Events have binary state (signaled or not signaled) and may be either
+   * automatically reset or manually reset. Automatic-reset events go to non-signaled state when a
+   * WaitForObject is woken up by the event; manual-reset events require ResetEvent() to be called
+   * to set the event to non-signaled state; if ResetEvent() is not called, any waiter on that event
+   * will immediately wake when called.
+   *
+   * @param manualReset true for manual reset, false for automatic reset
+   * @param initialState true to make the event initially in signaled state
+   * @return Event handle
+   */
   public static native int createEvent(boolean manualReset, boolean initialState);
 
+  /**
+   * Destroys an event. Destruction wakes up any waiters.
+   *
+   * @param eventHandle event handle
+   */
   public static native void destroyEvent(int eventHandle);
 
+  /**
+   * Sets an event to signaled state.
+   *
+   * @param eventHandle event handle
+   */
   public static native void setEvent(int eventHandle);
 
+  /**
+   * Sets an event to non-signaled state.
+   *
+   * @param eventHandle event handle
+   */
   public static native void resetEvent(int eventHandle);
 
+  /**
+   * Creates a semaphore. Semaphores keep an internal counter. Releasing the semaphore increases the
+   * count. A semaphore with a non-zero count is considered signaled. When a waiter wakes up it
+   * atomically decrements the count by 1. This is generally useful in a single-supplier,
+   * multiple-consumer scenario.
+   *
+   * @param initialCount initial value for the semaphore's internal counter
+   * @param maximumCount maximum value for the samephore's internal counter
+   * @return Semaphore handle
+   */
   public static native int createSemaphore(int initialCount, int maximumCount);
 
+  /**
+   * Destroys a semaphore. Destruction wakes up any waiters.
+   *
+   * @param semHandle semaphore handle
+   */
   public static native void destroySemaphore(int semHandle);
 
+  /**
+   * Releases N counts of a semaphore.
+   *
+   * @param semHandle semaphore handle
+   * @param releaseCount amount to add to semaphore's internal counter; must be positive
+   * @return True on successful release, false on failure (e.g. release count would exceed maximum
+   *     value, or handle invalid)
+   */
   public static native boolean releaseSemaphore(int semHandle, int releaseCount);
 
   static native long allocateRawFrame();