Eliminate side effects of a11y window title.

ag/898112 added passing the window title to accessibility. To do that,
it also updated copy of the title in WindowManager.LayoutParams. That
was a behavior change, and the change broke cts tests that enforce that
the title in LayoutParams matches its expected format.

This change restores the previous behavior and adds a separate field to
LayoutParams to old an up-to-date title to pass to accessibility.

Bug: 28002185
Change-Id: Ia5b549113600b7c4fcc80b76c3f3a944dddaf483