Strong type Value on DataBoundFormComponent<T>

[pianomanjh]

This updates the Value property of DataBoundFormComponent<T> to be of type T, for more canonical use, consistency, and ease of extension.
We have several custom controls that benefit from inheriting from this component, to better fit in the Radzen ecosystem. Needing to cast T when binding in these scenarios causes various difficulties, and is unnecessary as much as I can tell.

This should not result in any breaking changes, as users who are already casting this value to T will simply no longer need to.

Please let me know if I'm missing something as to the need for Value to be object vs T.

[akorchev]

This is a breaking change as some components support multiple selection and single selection. The value could be either T or IEnumerable depending on selection mode. I don't think we can accept this pull request.

[pianomanjh]

Can you share an example with me? I've tested this across the various multi/single select component demos. (ListBox/DropDown/DropDownDataGrid/etc)

[enchev]

DataGrid CheckBoxList filtering by first column