feat(ios): include built Carthage frameworks in keyman-engine-ios-x.y.z.zip

@davidmoore1 also wrote:

> I think I've finally found a way to get the engine built and into SAB without all the hassles I had to go through with Carthage. I created a repository with build scripts that clone the keyman repository, builds the engine, and then moves the xcframework, along with the Carthage frameworks that were generated, into a package that can be included via the XCode package dependency. And it builds through a github action, which should also simplify some things. I've got a little testing to complete after we get our next release out, but it seems to work correctly. So with that, all I need to do is specify the branch to use (like stable-17.0) and I can upgrade the engine to a new release without all of the changes I was having to make to get it to build for Carthage

_Originally posted by @mcdurdin in https://github.com/keymanapp/keyman/issues/11834#issuecomment-2817449040_

In terms of the Carthage pain, sounds like capturing the xcframework and the carthage frameworks as a build artifact from the Keyman build may be enough? Then you don't need to clone the Keyman repo at all, just download and unzip a .zip from [downloads.keyman.com](http://downloads.keyman.com/)? We could certainly add that easily enough into our build processes, and that would help other integrators also.

We already have keyman-engine-ios-x.y.z.zip in our release builds. But that does not include the other generated Carthage frameworks. If all we need to do is add those to that zip file, that'd be a big win. (We could generate the package as well.)