[WIP] Update Xcode version supported (9.x/10.x/...)

[brodycj]

Continuation from PR #386: show minimum Xcode version as 9.x (deprecated) or 10.

This is assuming that the issues with Xcode 10 discussed in #407 are resolved by the time we make the new release of cordova-ios.

P.S. Linking to apache/cordova-docs#863: Minimum Xcode version in cordova-docs & cordova-ios not consistent (sorry apache/cordova-docs#863 was an old issue, will raise a new issue to track this one)

[dpogue]

I wonder if we want to say we only officially support Xcode 10 (which will be required for app store submissions as of March 2019), but unofficially keep the project files working in Xcode 9 for at least the first release of the next major?

I don't especially want us to get into a situation where Xcode 9 is holding us back from fixing bugs, but I don't want to outright drop it while people are still using it. I don't really think supporting both will be a problem, but that could change with future Xcode (11, 12) versions.

If we don't explicitly claim to support Xcode 9, then we wouldn't have any obligation to do a major version bump if/when we break Xcode 9.

[brodycj]

If we want to drop Xcode 9 support, which I am starting to favor, then I would favor that we do something small that we know would break the build on Xcode 9.

I can imagine an Xcode 9 user doing an upgrade without reading the notes, and then someday boom!

I think it should be no problem to support both Xcode 9 and Xcode 10 in 4.x.x.

Another alternative could be to release cordova-ios@5 to drop Node.js 4 support, and then cordova-ios@6 to drop Xcode 9 support, before we finish releasing Cordova 9.

[brodycj]

I just marked this as a bug, linked to apache/cordova-docs#863 (minimum Xcode version in cordova-docs & cordova-ios not consistent) (sorry that was an old bug, I will raise a new issue to track this one).

[dpogue]

I think it should be no problem to support both Xcode 9 and Xcode 10 in 4.x.x.

Do you mean 5.x.x? I think it will be a problem to support Xcode 10 in 4.x.x (it currently doesn't work, and I don't think we can fix that without breaking Xcode 8 (which is supported by 4.x.x))

[brodycj]

I think it should be no problem to support both Xcode 9 and Xcode 10 in 4.x.x.

Do you mean 5.x.x?

I would favor supporting both Xcode 9 and Xcode 10 in 5.x.x.

I actually did not encounter any issues when testing my own work with cordova-ios@4.5.x and recent Xcode 10 upgrade. But yes I would favor that we retire cordova-ios@4 soon if possible.

I will raise a new issue to keep this consistent between cordova-ios and cordova-docs.