Fix use of Swift 6 language mode

[orobio]

Adds a Package@swift-6.0.swift to make sure the package is compiled for the Swift 6 language mode. This fixes the visibility of the new withSpan functions, gated by #if swift(>=6.0).

Not sure if this is the desired solution, but it currently works for us. Let me know if something else is required and I'll be happy to look into it.

Edit: After digging in some more, I think it would be better to update all #if swift(>=6.0) conditionals to #if compiler(>=6.0). Would that be an acceptable solution?

[Lukasa]

I think we should take your suggestion of updating to use #if compiler, not #if swift.

[orobio]

I think we should take your suggestion of updating to use #if compiler, not #if swift.

It's updated to use #if compiler. I just found a comment on the previous pull request, regarding the deprecation being done unconditionally. I feel we should have both @available... and @_disfavoredOverload inside the #if blocks. If you agree, I can push an update for that as well.

[Lukasa]

Yeah, I'm not wild about the deprecation being present when there is no alternative choice.

[orobio]

Yeah, I'm not wild about the deprecation being present when there is no alternative choice.

I pushed a fix for this as well.

[Lukasa]

@ktoso I think we need a review from you here

[ktoso]

Thanks for the ping! Coming out of sick leave inbox was overwhelmed 😅

[ktoso]

@swift-server-bot test this please

[ktoso]

docc plugin seems borked on 5.7? Seems weird 🤔 Need to investigate what's up

[jessezamora]

Anything new here?

[orobio]

Could this have been a temporary glitch? Should we perhaps run the test again?

[ktoso]

@swift-server-bot test this please

[ktoso]

Sorry I was traveling and only now catching up here, let's see what's up here

[ktoso]

@swift-server-bot test this please

[ktoso]

Thank you, I'll cut a 1.1.2 with this