XCFramework Support via CocoaPods

[sethfri]

Describe the bug

When importing gRPC via CocoaPods, it pulls in abseil, which is only available as a source pod. This means when we import gRPC into our app, we have to rebuild abseil every time we do a clean build. This adds a significant amount of time to our build times.

Apple has a native binary format called an XCFramework that would allow for abseil to be distributed as a binary pod, and CocoaPods plugins like cocoapods-pack exist to produce XCFrameworks from podspecs. If abseil was distributed as an XCFramework, we would be able to import it as a binary pod, which would speed up the builds for our app. This would be a boon for every iOS app that imports abseil.

What build system are you using?

CocoaPods and xcodebuild

Additional context

I have a sister issue open for gRPC at https://github.com/grpc/grpc/issues/28749

[derekmauro]

The CocoaPod is not made or supported by our team. @veblush probably knows the most about this.