Move check for cursor within Wine window to editor

We'll reuse this for the LeaveNotify check instead to avoid having to
ignore all `NonVirtual` events.

src/wine-host/editor.cpp

@@ -1245,4 +1245,31 @@ ATOM get_window_class() noexcept {
     return window_class_handle;
 }
 
+bool is_cursor_in_wine_window() noexcept {
+    static const HWND windows_desktop_window = GetDesktopWindow();
+
+    POINT windows_pointer_pos;
+    GetCursorPos(&windows_pointer_pos);
+    if (HWND windows_window = WindowFromPoint(windows_pointer_pos);
+        windows_window && windows_window != windows_desktop_window) {
+        // NOTE: Because resizing reparented Wine windows without XEmbed is
+        //       a bit janky, yabridge creates windows with client areas
+        //       large enough to fit the entire screen, and the plugin then
+        //       embeds its own GUI in a portion of that. The result is that
+        //       `WindowFromPoint()` will still return that same huge window
+        //       when we hover over an area to the right or to the bottom of
+        //       a plugin GUI. We can easily detect and skip that though,
+        //       since the embedded plugin windows won't have an X11 window
+        //       ID property.
+        const xcb_window_t x11_window =
+            static_cast<xcb_window_t>(reinterpret_cast<size_t>(
+                GetProp(windows_window, "__wine_x11_whole_window")));
+        if (x11_window == XCB_NONE) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
 #undef THROW_X11_ERROR