Switch to Microsoft.Extensions.Logging

[bgrainger]

MySqlConnector currently implements logging via a custom interface: #390

Npgsql is planning to replace their custom logging interface with Microsoft.Extensions.Logging (npgsql/npgsql#2103 (comment)):

Looking at this again, we should really consider switching to Microsoft.Extensions.Logging - there isn't any reason not to do that any more:

• It's the de-facto standard library in the .NET ecosystem
• It's definitely high-perf (used in ASP.NET itself), there's even new source generation support in .NET 6.0.
• It allows effortless logging to a wide variety of destinations; with Npgsql's custom logging, adapters need to be coded up manually every time.
  • This includes OpenTelemetry logging support.
• The only drawback I can think of is having to reference Microsoft.Extensions.Logging.Abstractions, which I don't love, but I think it makes sense at this point.

All those advantages (and the drawback) are the same for MySqlConnector, and I reach the same conclusion: it's time to switch.

I assume this would be a source+binary breaking change, so it would go in the next major version.

[bgrainger]

DbDataSource (dotnet/runtime#64812) could allow the ILoggerFactory to be specified.