atspi: use detail value of window activated signal

atspi: use detail value of window activated signal

The detail value of window activated signal is using for following cases

(1) support "default_label" attribute of window
(2) notify existing keyboard window.
The keyboard window would exist always, once it shows.
So if screen-reader turns off, and turn on again, there was no ATSPI signal.
We are using 'activate' signal for this case to get the reference of
keyboard window. And we are using detail value to reduce a call of IPC.

Change-Id: I11db347b89f283ad2ab7fd5378ca123948dbbaf5