Send onActivityUnpinned when Activity is force killed or crashed

It seems like it is possible for the task to be in pinned mode while
WindowContainer it is in no longer is in that mode, which leads to a
skipped invocation to notifyActivityPipModeChanged.

Bug: 294096108
Bug: 257519948
Test: manually
Test: launch an app, crash/force kill it, confirm callback is delivered
Test: before http://recall/-/ekEuGtt9d9HWqkUtAzpHx8/gBuDVFExNtbyDxL85YGYWu
Test: after http://recall/-/ekEuGtt9d9HWqkUtAzpHx8/cQE890lYS2oqh60zS9L9Y4

Change-Id: I1742b85423e3924121263d088756125ae35771aa