Add dylib for MacOS targets so that it can be installed via Homebrew

[ernieturner]

Our current Homebrew formula only installs a .a binary that will work for the iOS simulator and iOS devices. Ideally it would also install the .dylib necessary for MacOS to use it as well. Unfortunately installing these two binaries side-by-side causes errors in XCode because it just picks the dylib when running on an iOS device and then won't build. So in the meantime we've just published the .a.

We should update our formula so that it installs both the .a and .dylib files together and figure out how to get XCode to work. Once this is done we can also update the CI workflow in the Swift library to install the binary via Homebrew which will work on MacOS.