rARCd343be59269a

Error handling: send Deprecation messages as explicit Event

Summary:
Ref T15554. When a deprecation warning is captured here, mark it as such and send using the same channel as error messages.
Error Handlers will generally ignore it now, so they'll need to be updated, e.g. D25386

Test Plan:
Hitting a `strlen(null)` before This Change:

- Web:
- PhutilAggregateException - white boxes with red border.
- Daemons:
- trace in daemon log, task fails. Daemon sleeps for 5 seconds.
- Arcanist and Scripts…