asp-for taghelper not working properly in DisplayDrivers

[Skrypt]

As a follow up to #15488
When a custom validation is required in the UpdateEditorAsync method of a display driver.
The asp-for taghelper doesn't display the proper mutated value.
This can be fixed by updating the updater.ModelState in that method because this is what the asp-for taghelper uses to display a value.
We may find a better fix than updating manually the updater.ModelState.

    public override async Task<IDisplayResult> UpdateAsync(
        CreateSite model,
        ProjectDetails section,
        IUpdateModel updater,
        UpdateEditorContext context
    )
    {
        var viewModel = new ProjectDetailsViewModel();

        await context.Updater.TryUpdateModelAsync(viewModel, Prefix);

        section.ProjectName = viewModel.ProjectName.ToSafeName();

        // This is the fix to get the proper value to display with the asp-for taghelper
        context.Updater.ModelState.SetModelValue(
            $"{Prefix}.{nameof(section.ProjectName)}",
            section.ProjectName,
            section.ProjectName
        );

        // After removing special chars ProjectName could become an empty string.
        if (string.IsNullOrWhiteSpace(section.ProjectName))
        {
            updater.ModelState.AddModelError(Prefix, nameof(section.ProjectName), S["Project name is required"]);
        }
    }

@sebastienros @deanmarcussen