Make $wgMWLoggerDefaultSpi more expressive

Make $wgMWLoggerDefaultSpi more expressive

Allow $wgMWLoggerDefaultSpi to specify a more expressive object creation
by introducing a new ObjectFactory class which can process an array of
instructions to call either an object constructor or a factory method
with an array of arguments. This allows removal of the
$wgMWLoggerMonologSpiConfig global variable in favor of configuration
using $wgMWLoggerDefaultSpi.

New classes introduced:
; ObjectFactory
: Construct objects from configuration instructions.

Change-Id: If56cce5dcb1ad5712e238d6e2dab809a351f79be