patch 8.0.1123: cannot define a toolbar for a window

Problem:    Cannot define a toolbar for a window.
Solution:   Add a window-local toolbar.

src/structs.h

@@ -70,6 +70,10 @@ typedef int			scid_T;		/* script ID */
 typedef struct file_buffer	buf_T;  /* forward declaration */
 typedef struct terminal_S	term_T;
 
+#ifdef FEAT_MENU
+typedef struct VimMenu vimmenu_T;
+#endif
+
 /*
  * Reference to a buffer that stores the value of buf_free_count.
  * bufref_valid() only needs to check "buf" when the count differs.
@@ -2611,6 +2615,14 @@ struct matchitem
 #endif
 };
 
+#ifdef FEAT_MENU
+typedef struct {
+    int		wb_startcol;
+    int		wb_endcol;
+    vimmenu_T	*wb_menu;
+} winbar_item_T;
+#endif
+
 /*
  * Structure which contains all information that belongs to a window
  *
@@ -2686,7 +2698,7 @@ struct window_S
      */
     int		w_winrow;	    /* first row of window in screen */
     int		w_height;	    /* number of rows in window, excluding
-				       status/command line(s) */
+				       status/command/winbar line(s) */
     int		w_status_height;    /* number of status lines (0 or 1) */
     int		w_wincol;	    /* Leftmost column of window in screen.
 				       use W_WINCOL() */
@@ -2798,6 +2810,12 @@ struct window_S
 
     char_u	*w_localdir;	    /* absolute path of local directory or
 				       NULL */
+#ifdef FEAT_MENU
+    vimmenu_T	*w_winbar;	    /* The root of the WinBar menu hierarchy. */
+    winbar_item_T *w_winbar_items;  /* list of items in the WinBar */
+    int		w_winbar_height;    /* 1 if there is a window toolbar */
+#endif
+
     /*
      * Options local to a window.
      * They are local because they influence the layout of the window or
@@ -3064,8 +3082,6 @@ typedef struct cursor_entry
 /* Start a menu name with this to not include it on the main menu bar */
 #define MNU_HIDDEN_CHAR		']'
 
-typedef struct VimMenu vimmenu_T;
-
 struct VimMenu
 {
     int		modes;		    /* Which modes is this menu visible for? */