platform/windows: add optional DwmFlush() call to improve Windows capture

Invoke DwmFlush() before acquiring the next frame to alleviate visual stutter
during mouse movement at the cost of constraining the capture rate to the host's
monitor refresh.

Disabled by default; enable via "dwmflush" boolean configuration parameter.

docs/source/about/advanced_usage.rst

@@ -333,6 +333,25 @@ Example
         3840x1600,
       ]
 
+dwmflush
+^^^^^^^^
+
+Description
+   Invoke DwmFlush() to sync screen capture to the Windows presentation interval.
+
+   .. Caution:: Applies to Windows only. Alleviates visual stuttering during mouse movement, but causes the capture
+      rate to be limited to the host monitor's currently active refresh rate.
+
+Default
+   ``disabled``
+
+Examples
+
+   Windows
+      .. code-block:: text
+
+         dwmflush = enabled
+
 Audio
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