fpspreadsheet: Redo storage of formulas: formulas now are stored in a separate tree independent of the cells tree. The field FormulaValue of TCell record was removed. All unit tests passed. Demos updated (issues of speedtest due to SST in BIFF8 found - not related).

git-svn-id: https://svn.code.sf.net/p/lazarus-ccr/svn@6446 8e941d3f-bd1b-0410-a28a-d453659cc2b4

components/fpspreadsheet/examples/other/demo_expression_parser.pas

@@ -51,7 +51,7 @@ begin
     parser := TsSpreadsheetParser.Create(worksheet);
     try
       try
-        parser.Expression := cell^.FormulaValue;
+        parser.Expression := worksheet.ReadFormula(cell);
         res := parser.Evaluate;
 
         WriteLn('A2: ', parser.Expression);