Added 'dumpsys activity lastanr'

Allows for dumping the activity state during the last anr. This will
also be included in collected bug reports.

Bug: 38121026
Test: Cause an anr to occur and run 'adb shell dumpsys activity lastanr'
Change-Id: I1e4200f9e5cc16bfab98e5af31fc599cdd54cd11