patch 8.2.4724: current instance of last search pattern not easily spotted

Problem:    Current instance of last search pattern not easily spotted.
Solution:   Add CurSearch highlighting. (closes #10133)

src/structs.h

@@ -3329,6 +3329,7 @@ typedef struct
 			    // found match (may continue in next line)
     buf_T	*buf;	    // the buffer to search for a match
     linenr_T	lnum;	    // the line to search for a match
+    linenr_T	lines;	    // number of lines starting from lnum
     int		attr;	    // attributes to be used for a match
     int		attr_cur;   // attributes currently active in win_line()
     linenr_T	first_lnum; // first lnum to search for multi-line pat