Remove non-UTF8 characters from string fields.

The string type in the tombstone proto does not support non-UTF8
characters. Therefore, use the oct_encode function to encode the
abort_message field and message field from LogMessage.

Fix up stl includes, add ones that were missing and remove those not
being used.

Add new unit test to verify that the abort and log messages are
sanitized.

Bug: 279496937
Bug: 377940849
Bug: 378185483

Test: All unit tests pass.
Test: Ran pbtombstone on a crash with non-UTF8 characters and verified
Test: it processes properly after this change and fails before the change.
Change-Id: I3554d56caf9fcbfc410b4d554f6c3b4888b37e28