dumpstate: Add historical ANRs as separate entries in the zip file.

ANRs now show up as separate entries in the bugreport zip file, like so:

-rw----     0.0 fat   516946 bl    48779 defN 17-Jul-27 10:47 FS/data/anr/anr_2017-07-27-10-47-45-798
-rw----     0.0 fat   520627 bl    48995 defN 17-Jul-27 10:47 FS/data/anr/anr_2017-07-27-10-47-30-328

Bug: 32470528
Test: adb bugreport ./bugreport.zip; zipinfo -l ./bugreport.zip | grep anr

Change-Id: Ibcde7bd35cab1d81e26c72e9247d63cf7bce1504