This removes the need to call QLoggingCategory::setFilterRules()
in the program code to default to disabled debug type log
without any other settings.
The latter has disadvantages, as it shadows any settings done
in qtlogging.ini config files by the user
(e.g. via kdebugsettings), thus enabling runtime control only
via QT_LOGGING_CONF/QT_LOGGING_RULES, which is not that
comfortable with lots of categories.
Also use ECMQtDeclareLoggingCategory for less manual code
While there can be some inconsistency with the default disabled
log categories by ECMQtDeclareLoggingCategory, which
switched to QtInfoMsg for ECM 5.26 (when KF5 5.26 has Qt 5.5
as min dep, which is the Qt version QtInfoMsg was added),
current KDevPlatform code has Qt 5.4 as minimum version and
thus also does not use qCInfo, so KDevPlatform behaviour should
be the same across used Qt versions.