Windows: Throttle VBlankThread when the display is off

When the display goes to sleep IDXGIOutput::WaitForVBlank returns S_OK
immediately causing the VBlankThread to consume a core entirely with the
VBlank related messaging.

To limit this problem, we use the same technique as Chromium presently
does, and we sleep for 1 ms, if the time between the last two VBlank
events was less than a ms. This limits the VBlankThread messaging rate
of about 50.000/s on an Intel 13600 to 1000/s.

modules/juce_gui_basics/native/juce_VBlank_windows.cpp

@@ -121,6 +121,12 @@ private:
         {
             if (output->WaitForVBlank() == S_OK)
             {
+                if (const auto now = Time::getMillisecondCounterHiRes();
+                    now - std::exchange (lastVBlankEvent, now) < 1.0)
+                {
+                    Thread::sleep (1);
+                }
+
                 std::unique_lock lock { mutex };
                 condvar.wait (lock, [this] { return threadState != ThreadState::sleep; });
 
@@ -164,6 +170,7 @@ private:
         exit,
     };
 
+    double lastVBlankEvent = 0.0;
     ThreadState threadState = ThreadState::paint;
     std::condition_variable condvar;
     std::mutex mutex;