Add a dedicated function to dump incident report

Capturing incident report in dumpstate used to be bundled in dumpsys
proto, which was inflexible and subject to 10s time limit.
This patch creates a dedicated function in dumpstate to dump incident
report proto. It takes around 15s to complete on a new device.
Bug: 137493082
Test: Manually takes a bugreport from command line, power button, and
      BetterBug. Verifies /proto/incident_report.proto exists in the
      zip file, and no unintended avc denial.

Change-Id: Ia253e24afda4a7c1ef92fc564df465311be6fe3a