patch 9.1.0037: Calling get_breakindent_win() repeatedly when computing virtcol

Problem:  Calling get_breakindent_win() repeatedly when computing
          virtual column, and get_breakindent_win() does a STRCMP() on
          the whole line since patch 9.0.0016.
Solution: Cache the result, since the line doesn't change.
          (zeertzjq)

closes: #13879

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/structs.h b/src/structs.h
index da8c2e2..76f1433 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -4909,6 +4909,10 @@
     win_T	*cts_win;
     char_u	*cts_line;		// start of the line
     char_u	*cts_ptr;		// current position in line
+#ifdef FEAT_LINEBREAK
+    int		cts_bri_size;		// cached size of 'breakindent', or -1
+					// if not computed yet
+#endif
 #ifdef FEAT_PROP_POPUP
     int		cts_text_prop_count;	// number of text props; when zero
 					// cts_text_props is not used