patch 8.1.2371: FEAT_TEXT_PROP is a confusing name

Problem:    FEAT_TEXT_PROP is a confusing name.
Solution:   Use FEAT_PROP_POPUP. (Naruhiko Nishino, closes #5291)
diff --git a/src/structs.h b/src/structs.h
index d851a27..3e5be69 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -2119,7 +2119,7 @@
 //  # define CRYPT_NOT_INPLACE 1
 #endif
 
-#ifdef FEAT_TEXT_PROP
+#ifdef FEAT_PROP_POPUP
 typedef enum {
     POPPOS_BOTLEFT,
     POPPOS_TOPLEFT,
@@ -2615,7 +2615,7 @@
     listener_T	*b_listener;
     list_T	*b_recorded_changes;
 #endif
-#ifdef FEAT_TEXT_PROP
+#ifdef FEAT_PROP_POPUP
     int		b_has_textprop;	// TRUE when text props were added
     hashtab_T	*b_proptypes;	// text property types local to buffer
 #endif
@@ -2768,7 +2768,7 @@
     win_T	    *tp_prevwin;    // previous window in this Tab page
     win_T	    *tp_firstwin;   // first window in this Tab page
     win_T	    *tp_lastwin;    // last window in this Tab page
-#ifdef FEAT_TEXT_PROP
+#ifdef FEAT_PROP_POPUP
     win_T	    *tp_first_popupwin; // first popup window in this Tab page
 #endif
     long	    tp_old_Rows;    // Rows when Tab page was left
@@ -3020,7 +3020,7 @@
     int		w_width;	    // Width of window, excluding separation.
     int		w_vsep_width;	    // Number of separator columns (0 or 1).
     pos_save_T	w_save_cursor;	    // backup of cursor pos and topline
-#ifdef FEAT_TEXT_PROP
+#ifdef FEAT_PROP_POPUP
     int		w_popup_flags;	    // POPF_ values
     int		w_popup_handled;    // POPUP_HANDLE[0-9] flags
     char_u	*w_popup_title;