Add udp2log compatible log handler

The MwLogHandler replicates the behavior of MediaWiki's wfErrorLog()
global method when a `udp://HOST:PORT[/PREFIX]` URI is specified as the
log destination. Otherwise it behaves similar to Monolog's
StreamHandler.

Bug: 57954
Change-Id: I85d61a0df0a3447c17c223e47566afee39007fc7
Merge "Add udp2log compatible log handler"