patch 8.1.1928: popup windows don't move with the text when making changes

Problem:    Popup windows don't move with the text when making changes.
Solution:   Add the 'textprop" property to the popup window options, position
            the popup relative to a text property. (closes #4560)
            No tests yet.
diff --git a/src/proto/move.pro b/src/proto/move.pro
index c2ec8d5..d05eb17 100644
--- a/src/proto/move.pro
+++ b/src/proto/move.pro
@@ -27,6 +27,7 @@
 int win_col_off2(win_T *wp);
 int curwin_col_off2(void);
 void curs_columns(int may_scroll);
+void textpos2screenpos(win_T *wp, pos_T *pos, int *rowp, int *scolp, int *ccolp, int *ecolp);
 void f_screenpos(typval_T *argvars, typval_T *rettv);
 void scrolldown(long line_count, int byfold);
 void scrollup(long line_count, int byfold);