Improvements

• #6056 FileTarget - Archive Cleanup sort filenames using natural ordering. (@snakefoot)
• #6054 EventProperties - Format Dictionary Properties correctly. (@snakefoot)
• #6051 Failure to create config item should be reported as InternalLogger Error. (@snakefoot)
• #6052 PropertiesDictionary - Faster TryGetValue without IsEmpty. (@snakefoot)
• #6048 PropertiesDictionary - Increase initial capacity when insert. (@snakefoot)
• #6047 LogEventInfo - Minor optimization of HasImmutableProperties. (@snakefoot)
• #6057 WhenEmpty - Support AppDomainFixedOutput optimization. (@snakefoot)
• #6053 JsonAttribute - Reduce code complexity when Encode = false. (@snakefoot)
• #6044 Target also enforce PreventMultipleCalls when WriteFailedNotInitialized. (@snakefoot)
• #6042 NLog.RegEx - Fixed Wiki-link in nuget-package. (@snakefoot)