Save window when an app died while it's visible

- If an app died visible, keep the dead window and leave it on screen.

- Apply 50% dim over the dead window to indicate it's no longer active.

- Monitor touch inputs on the dead window and restart the app on tap.

bug: 24913379
Change-Id: I911da4e6135f2bffaf3b1bbe6f911ff689a278ff