Use number of displayed, and not document, lines in the map code

We really care about the number of physical, i.e. "display", lines
appearing in the window and not the number of logical, or "document",
lines.

They are the same as long as no lines are either wrapped or folded but
become different as soon as either of them is used.

samples/stc/stctest.cpp

@@ -1045,6 +1045,13 @@ private:
         m_editVisibleLines = m_edit->LinesOnScreen();
     }
 
+    // Get the total number of displayed lines, i.e. not taking hidden lines
+    // (due to folding) into account and counting wrapped lines.
+    int GetDisplayedLineCount() const
+    {
+        return VisibleFromDocLine(GetLineCount());
+    }
+
     // Get map line at the given mouse position.
     int GetMapLineAtPoint(const wxPoint& pos) const
     {
@@ -1058,7 +1065,7 @@ private:
         if ( firstLine < 0 )
             return 0;
 
-        auto const lastValid = GetLineCount() - m_editVisibleLines;
+        auto const lastValid = GetDisplayedLineCount() - m_editVisibleLines;
         if ( firstLine > lastValid )
             return lastValid;
 
@@ -1106,7 +1113,7 @@ private:
     // Scroll the editor to correspond to the current position in the map.
     void SyncEditPosition()
     {
-        auto const totalLines = GetLineCount();
+        auto const totalLines = GetDisplayedLineCount();
 
         if ( m_editVisibleLines >= totalLines )
         {
@@ -1128,7 +1135,7 @@ private:
     void SyncMapPosition()
     {
         // First check for the special case when all lines are visible.
-        auto const totalLines = GetLineCount();
+        auto const totalLines = GetDisplayedLineCount();
         if ( m_editVisibleLines >= totalLines )
         {
             SetMapFirstVisibleLine(0);
@@ -1295,7 +1302,7 @@ private:
         // mapFirst = α * editorFirst, we can compute the new editor first
         // line as thumbTopPos / ((1 - α) * mapLineHeight) or the map first
         // line as thumbTopPos / ((1/α - 1) * mapLineHeight).
-        auto const totalLines = GetLineCount();
+        auto const totalLines = GetDisplayedLineCount();
 
         SetEditFirstVisibleLine
         (