vendor: import KillerPDF 1.7.5 source (GPL-3.0) as the base for MMD PDF

Models/LinkTypes.cs

@@ -0,0 +1,17 @@
+namespace KillerPDF
+{
+    /// <summary>
+    /// One link rectangle on a page, in render-dim coordinates.
+    ///
+    /// Used by the tiled views (continuous, grid, two-page), where a per-link overlay would swallow
+    /// the click without its own handler ever firing - so clicks and the hover cursor are resolved
+    /// by bounds-testing these rects instead. That makes them the source of truth for links outside
+    /// single-page view.
+    ///
+    /// TOP-LEVEL, not nested. Links.cs lives in the viewer control while ContextMenu.cs lives on the
+    /// window and also bounds-tests these rects to build the right-click menu, so neither class can
+    /// own the type.
+    /// </summary>
+    internal readonly record struct LinkInfo(
+        double Cx, double Cy, double Cw, double Ch, object Tag, string Tip, int AnnotIndex);
+}