Windows API封装：自动向目标窗口发送文本

#region 向光标所在输入框输入指定内容
    [StructLayout(LayoutKind.Sequential)]
    public struct RECT
    {
        int left;
        int top;
        int right;
        int bottom;
    }
    public class SendMsg
    {
        [DllImport("user32.dll")]
        public static extern IntPtr GetForegroundWindow();
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        public static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
        [DllImport("user32.dll")]
        static extern uint GetWindowThreadProcessId(IntPtr hWnd, IntPtr ProcessId);
        [DllImport("user32.dll")]
        static extern bool GetGUIThreadInfo(uint idThread, ref GUITHREADINFO lpgui);
        [StructLayout(LayoutKind.Sequential)]
        public struct GUITHREADINFO
        {
            public int cbSize;
            public int flags;
            public IntPtr hwndActive;
            public IntPtr hwndFocus;
            public IntPtr hwndCapture;
            public IntPtr hwndMenuOwner;
            public IntPtr hwndMoveSize;
            public IntPtr hwndCaret;