Add ChannelPipeline.SynchronousOperations.Position

[0xTim]

Adds a new ChannelPipeline.SynchronousOperations.Position type to fill a hole in the API that prevented non-sendable Channel handlers being added at a position to the pipeline via the synchronous operations.

[0xTim]

@Lukasa I've updated the existing public APIs to use the new type to avoid confusing the compiler since the APIs are not usable in their current form. It you'd prefer all the existing APIs to be deprecated and add @_disfavoredOverload instead I can do that

[Lukasa]

Thanks Tim. Yeah, can we use overloads and @_disfavoredOverload? I think it would also be enough to deprecate the old APIs: you can easily test that by omitting the disfavored overload keyword and confirming everything still compiles without warnings.

[0xTim]

Updated - I was getting compiler errors due to "ambiguous references..." without the disfavoured overloads so added them in

[Lukasa]

Thanks for this! I've left a few notes in the diff.

[0xTim]

@Lukasa all these should be fixed now

[Lukasa]

Ok great, this looks really good. One quick note though, can we add a few very simple tests of these new APIs? Just inserting handlers and confirming they're there is sufficient.

[0xTim]

Ok great, this looks really good. One quick note though, can we add a few very simple tests of these new APIs? Just inserting handlers and confirming they're there is sufficient.

Yes that would be helpful - added!

[Lukasa]

Ok, this LGTM. Let's see what CI says.

[Lukasa]

Looks like the format check wants some cleanups, mind tackling that for me?

[0xTim]

Done