patch 9.1.0172: More code can use ml_get_buf_len() instead of STRLEN()

Problem:  More code can use ml_get_buf_len() instead of STRLEN().
Solution: Change more STRLEN() calls to ml_get_buf_len().  Also do not
          set ml_line_textlen in ml_replace_len() if "has_props" is set,
          because "len_arg" also includes the size of text properties in
          that case. (zeertzjq)

closes: #14183

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/proto/memline.pro b/src/proto/memline.pro
index eb21a7e..c5d9b5d 100644
--- a/src/proto/memline.pro
+++ b/src/proto/memline.pro
@@ -20,6 +20,7 @@
 char_u *ml_get_curline(void);
 char_u *ml_get_cursor(void);
 colnr_T ml_get_len(linenr_T lnum);
+colnr_T ml_get_pos_len(pos_T *pos);
 colnr_T ml_get_curline_len(void);
 colnr_T ml_get_cursor_len(void);
 colnr_T ml_get_buf_len(buf_T *buf, linenr_T lnum);