[FluentDesignTheme] Add OnLoaded event

[dvoituron]

[FluentDesignTheme] Add OnLoaded event

Add an OnLoaded event raised when the component is rendered for the first time.
This event contains all properties initialized: Mode, IsDark, CustomColor, OfficeColor, StorageName, Direction.

Two new JavaScript properties are added: Blazor.theme.isDarkMode() and Blazor.theme.isSystemDark()

Example

<FluentDesignTheme OnLoaded="@OnLoaded"
                   OnLuminanceChanged="@OnLuminanceChanged" />

@code
{
    void OnLoaded(LoadedEventArgs e)
    {
        DemoLogger.WriteLine($"Loaded: {(e.Mode == DesignThemeModes.System ? "System" : "")} {(e.IsDark ? "Dark" : "Light")}");
    }

    void OnLuminanceChanged(LuminanceChangedEventArgs e)
    {
        DemoLogger.WriteLine($"Changed: {(e.Mode == DesignThemeModes.System ? "System" : "")} {(e.IsDark ? "Dark" : "Light")}");
    }
}

[github-actions]

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