Replace log4net with Microsoft.Extensions.Logging.Abstractions

[ltrzesniewski]

This replaces log4net (which is dormant) with the Microsoft.Extensions.Logging.Abstractions package.

You now have to set the ZebusLogManager.LoggerFactory static property in order to get logs from Zebus. Further changes to this property will be picked up (which is how you can notify BusMessageLogger that the underlying logging configuration changed).

Additional notes:

• I could have implemented the log4net interface on top of ILogger using extension methods, but using the real API seemed cleaner.
• I didn't use the string interpolation feature of the package, but used interpolated strings ($"...") instead in order to avoid additional string parsing and impacting the formatter cache.
• A simple log factory on top of log4net is provided in the demo directory runner.
• Maybe we should add a separate ZebusLogManager.NotifyConfigurationChanged() method in order to notify BusMessageLogger to reload its cache?

[ocoanet]

Thank you for this PR. I like the fact that you replaced string formats by interpolated strings.

nitpick: The Log4NetConfigurator types were helpful to understand complex unit tests and they will be missed. Do you really think they should be removed?

[ocoanet]

You had to implement this? There is no built-in Log4NetLoggerFactory?

[ltrzesniewski]

log4net doesn't reference Microsoft.Extensions.Logging.Abstractions, so there's nothing built-in

[ocoanet]

question: Why did you choose to expose ILoggerFactory and not ILoggerProvider?

[ltrzesniewski]

ILoggerFactory seemed to be the standard approach, and it's conceptually more high-level.

[alexandrekow]

@ltrzesniewski
I think it would be a nice addition to use Log message template instead of interpolated string.
It will make the way for structured logging.

[ltrzesniewski]

I mentioned this in the issue:

I didn't use the string interpolation feature of the package, but used interpolated strings ($"...") instead in order to avoid additional string parsing and impacting the formatter cache.

The implementation in the package adds some overhead since it parses the string in order to convert it to an argument to String.Format, and caches the resulting formatter. If the cache size reaches a max value, then the string gets parsed every time... I wanted to avoid that.
Also, the structured logging approach we started using in our codebase is different. We may revisit this in the future if we want to extend it.