`SortExpression` for grids should be reworked

[acizmarik]

There is one more place where I need to fix this. ISortingOptions.SortExpression can be populated with DateTimeProperty.ToBrowserLocalTime() when user tries to sort by specifying AllowSorting="true" and clicking on the column within a grid.

However, it is going to be separate PR as it is handled a bit differently there

Originally posted by @acizmarik in https://github.com/riganti/dotvvm/issues/1385#issuecomment-1142089083