First release of helper binary for Index while building V2

This is the first release of the helper binary described in the design document of index-while-building V2
https://github.com/bazel-ios/rules_ios/blob/9d545be02bd26544c9faebc5b073f937622f3166/docs/index_while_building.md

• Patches from MobileNativeFoundation#53
• Needed for bazelbuild/rules_swift#567 and bazelbuild/rules_swift#561

Longer term we'll should only need the helper binary to remap remotely compiled index data