patch 9.0.0918: MS-Windows: modifier keys do not work with mouse scroll event

Problem:    MS-Windows: modifier keys do not work with mouse scroll events.
Solution:   Use K_SPECIAL instead of CSI for the modifier keys. (Christopher
            Plewright, closes #11587)

src/term.c

@@ -5125,7 +5125,7 @@ handle_csi(
 			    csi_len, offset, buf, bufsize, buflen);
     }
 
-    // Key without modifier (bad Kitty may send this):
+    // Key without modifier (Kitty sends this for Esc):
     //	{lead}{key}u
     else if (argc == 1 && trail == 'u')
     {
@@ -5456,6 +5456,23 @@ check_termcode(
 	}
 	else
 #endif // FEAT_GUI
+#ifdef MSWIN
+	    if (len >= 3 && tp[0] == CSI && tp[1] == KS_EXTRA
+		    && (tp[2] == KE_MOUSEUP
+			|| tp[2] == KE_MOUSEDOWN
+			|| tp[2] == KE_MOUSELEFT
+			|| tp[2] == KE_MOUSERIGHT))
+	{
+	    // MS-Windows console sends mouse scroll events encoded:
+	    // - CSI
+	    // - KS_EXTRA
+	    // - {KE_MOUSE[UP|DOWN|LEFT|RIGHT]}
+	    slen = 3;
+	    key_name[0] = tp[1];
+	    key_name[1] = tp[2];
+	}
+	else
+#endif
 	{
 	    int  mouse_index_found = -1;