fix: When data binding, Value is not updated before @onchange is called

[mrpmorris]

Example: In the demos layout

1. A Task.Delay is required to allow the binding to occur before we know the value.

    public async void SwitchTheme()
    {
        await Task.Delay(50);

2. The code is tracking state rather than using the field _ltr that is bound to.

    public async Task SwitchDirection()
    {
        dir = (dir == LocalizationDirection.rtl) ? LocalizationDirection.ltr : LocalizationDirection.rtl;

This was a problem that was solved in .Net 7 when @bind-Value:after was introduced. However, because we need to continue to support .Net 6 this cannot be used.

[vnbaaij]

Fixed with #473