UI: On Win11 Use WM Window Decoration Styles API

On Windows 11 use the new WM Window Decoration Styles API, introduced
in ce42d92503. This will match the OS Title bar color to  that of the
main window top bar and also do similar color matching with content
in separate windows like Preferences. Note that this will not have any
effect on versions of Windows prior to 11.

Pull Request: https://projects.blender.org/blender/blender/pulls/134054

intern/ghost/intern/GHOST_SystemWin32.cc

@@ -586,10 +586,7 @@ GHOST_TCapabilityFlag GHOST_SystemWin32::getCapabilities() const
   return GHOST_TCapabilityFlag(GHOST_CAPABILITY_FLAG_ALL &
                                ~(
                                    /* WIN32 has no support for a primary selection clipboard. */
-                                   GHOST_kCapabilityPrimaryClipboard |
-                                   /* This WIN32 backend has not yet implemented support for window
-                                    * decoration styles. */
-                                   GHOST_kCapabilityWindowDecorationStyles));
+                                   GHOST_kCapabilityPrimaryClipboard));
 }
 
 GHOST_TSuccess GHOST_SystemWin32::init()

intern/ghost/intern/GHOST_WindowWin32.cc

@@ -403,6 +403,23 @@ std::string GHOST_WindowWin32::getTitle() const
   return title;
 }
 
+GHOST_TSuccess GHOST_WindowWin32::applyWindowDecorationStyle()
+{
+  /* DWMWINDOWATTRIBUTE::DWMWA_CAPTION_COLOR */
+  constexpr DWORD caption_color_attr = 35;
+
+  if (m_windowDecorationStyleFlags & GHOST_kDecorationColoredTitleBar) {
+    const float *color = m_windowDecorationStyleSettings.colored_titlebar_bg_color;
+    const COLORREF colorref = RGB(
+        char(color[0] * 255.0f), char(color[1] * 255.0f), char(color[2] * 255.0f));
+    if (!SUCCEEDED(DwmSetWindowAttribute(m_hWnd, caption_color_attr, &colorref, sizeof(colorref))))
+    {
+      return GHOST_kFailure;
+    }
+  }
+  return GHOST_kSuccess;
+}
+
 void GHOST_WindowWin32::getWindowBounds(GHOST_Rect &bounds) const
 {
   RECT rect;

intern/ghost/intern/GHOST_WindowWin32.hh

@@ -127,6 +127,11 @@ class GHOST_WindowWin32 : public GHOST_Window {
    */
   std::string getTitle() const;
 
+  /**
+   * Apply the window decoration style using the current flags and settings.
+   */
+  GHOST_TSuccess applyWindowDecorationStyle() override;
+
   /**
    * Returns the window rectangle dimensions.
    * The dimensions are given in screen coordinates that are