Persisted log parser for incident reporting

Add persisted log section (section 1116) in incident report. Since
persisted logs are only stored in /data/misc/logd in plain text
format with interleaving log buffers, incidentd must use a dedicated
parser to parse them into protobuf, and it is more efficient to store
all buffers in a single section.

Implementation details: incidentd invokes incident-helper-cmd, who
reads all persisted log files in /data/misc/logd dir matching
logcat.* pattern, parses them line by line into TextLogEntry, and
passes the data back to incidentd through stdout in protobuf wire
format.

Command to invoke persisted log directly:
$ incident-helper-cmd run persisted_logs

Bug: 146086597
Test: adb shell incident -p EXPLICIT 1116 | \
      .out/soong/host/linux-x86/bin/aprotoc --decode_raw
Change-Id: I163cc47f1b34a58b404d7b7485ff47d8893e3bdd