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/charset.c b/src/charset.c
index 0e4dbbe..3ea2ecb 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -971,6 +971,9 @@
     cts->cts_vcol = col;
     cts->cts_line = line;
     cts->cts_ptr = ptr;
+#ifdef FEAT_LINEBREAK
+    cts->cts_bri_size = -1;
+#endif
 #ifdef FEAT_PROP_POPUP
     if (lnum > 0 && !ignore_text_props)
     {
@@ -1282,7 +1285,11 @@
 	    if (*sbr != NUL)
 		head_prev += vim_strsize(sbr);
 	    if (wp->w_p_bri)
-		head_prev += get_breakindent_win(wp, line);
+	    {
+		if (cts->cts_bri_size < 0)
+		    cts->cts_bri_size = get_breakindent_win(wp, line);
+		head_prev += cts->cts_bri_size;
+	    }
 	    if (wcol < head_prev)
 	    {
 		head_prev -= wcol;
@@ -1303,7 +1310,11 @@
 	    if (*sbr != NUL)
 		head_mid += vim_strsize(sbr);
 	    if (wp->w_p_bri)
-		head_mid += get_breakindent_win(wp, line);
+	    {
+		if (cts->cts_bri_size < 0)
+		    cts->cts_bri_size = get_breakindent_win(wp, line);
+		head_mid += cts->cts_bri_size;
+	    }
 	    if (head_mid > 0 && wcol + size > wp->w_width)
 	    {
 		// Calculate effective window width.