Determines if the form containing this form manager is the active form. This will also return true if any owned forms are active. If this is overridden in derived classes, it should call the base implementation first. If the base returns false, additional processing should be used to determine if the form or owned forms are active.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
