Introduce WM#LayoutParams mWindowContextToken

The window context token is passed to the server side by attaching
to the layout params in WM#addView to receive configuration changes.

Bug: 159767464
Bug: 153369119
Test: atest
WindowContextTest#testCreateWindowContextWindowManagerAttachClientToken

Change-Id: I658b09727b42eb9c2fa2cea63f8a312761e0a9aa