StructuredLogEvent does not satisfy a common approach for TState of ILogger

The current implementation of `StructuredLogEvent` does not satisfy the common approach for `TState` provided for logger. The usual one provides the formatting message as the last one key value pair as visible below

https://github.com/dotnet/runtime/blob/ce99c5658cc8c6ef426f54864d394ba443820840/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/LoggerMessage.cs#L504-L531

while the `StructuredLogEvent` returns only the properties with `StructuredLogFieldAttribute`.

https://github.com/Azure/durabletask/blob/8d45ab7428c8e51f95d04a6a601a02e860451108/src/DurableTask.Core/Logging/StructuredLogEvent.cs#L99-L122

What's the reason for this discrepancy?

Additional note: in the [ApplicationInsights logger](https://github.com/microsoft/ApplicationInsights-dotnet/blob/a350e899e7690126dcea64c37ef936b92908a295/LOGGING/src/ILogger/ApplicationInsightsLogger.cs#L94) the `formatter` is used anyway, but other logging tools might be just lacking this information.

It would be nice to have it clarified and documented. The current approach for logging could be probably slimmed, if we get this cleared, but the potential work requires clarifying the assumptions behind this decision. The best answer, that the author of this question could dream about would be, _yes, let's align logging with the base logging packages_ 😉