ComboBox - allow to auto-select first value and check that the value is really in the collection

[tomasherceg]

We should add the AutoSelectFirstValue to the ComboBox control, because currently you have to initialize the SelectedValue property yourself in the viewmodel.

Also, a property ValidateSelectedValue would be useful - the ComboBox could check that the SelectedValue is really present in the DataSource collection, and throw an exception.

[tomasherceg]

This works automatically on the client side.
On the server side, the control should validate the value and add an error in the ModelState when the ValidateSelectedValue property is true.

[tomasherceg]

In order to preserve the remains of my mental integrity, most of which I have lost when digging into Knockout JS source codes of the options binding, I am closing this issue and I promise that I will never suggest any ComboBox enhancements.

The hell is real and closer that you might expect.