Support producing static XCFrameworks that is importable from Swift

Assuming this would fall into `framework_type = ["static"]` (not sure why this is a list) in the `apple_xcframework` rule.

In the meantime, users can use `apple_static_xcframework` with a post-process to add module map files, but note that XCFrameworks produced this way aren't usable as-is from normal Xcode Swift projects.

Start with the apple_xcframework rule and its framework_type setting, then compare it with apple_static_xcframework. Review how the current post-process adds module map files and verify the resulting XCFramework in a normal Xcode Swift project. Done means static XCFrameworks from apple_xcframework are directly importable from Swift.

Written by the indexing model from the issue text.