LoggingConfigurationParser - Added support for using assembly-name in type-name (comma delimiter)

[snakefoot]

Follow up to #4300, so instead you can do this:

<targets>
   <target name="evt" type="EventLog, NLog.WindowsEventLog" />
</targets>

Or like this:

<targets>
   <target name="elmah" type="elmah.io, Elmah.Io.NLog" />
</targets>

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

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0.0% Duplication

[snakefoot]

Updated wiki: https://github.com/NLog/NLog/wiki/Register-your-custom-component with using fully qualified name.

[snakefoot]

Updated wiki: https://github.com/NLog/NLog/wiki/Configuration-file#extensions about using fully qualified type-name.

[snakefoot]

It seems that using Elmah.Io.NLog, elmah.io in xsi:type is not valid format, when using XML-schema-validation.

It complains that , (Hexidecimal value 0x2C) is not acceptable. See also #4978