Fix WindowContextTests

Previously, window token assigns last config to mLastReportedConfiguration
directly, which makes it share the same reference with getConfiguration(),
and blocks all config changes request to clients.

This CL uses Configuration#setTo instead.

fixes: 152227175
Bug: 150251036
Test: atest WindowContextTests

Change-Id: I44143aa558f223eb301e28f2e9110bfd66eac636