Add script to clean up generated frameworks

[anaisbetts]

The framework generated by build.swift out of the box needs some work to be compatible with codesign. This commit adds a script that adds in the expected "Versions" folder similar to frameworks generated by Xcode.

Will take any and all feedback / improvements on my poor Bash scripting :)

TODO:

• macOS build links and codesigns in app
• iOS build links and codesigns in app
• iOS app can load in simulator

Closes #455

[anaisbetts]

This is looking mostly good, but I'm still having trouble generating an Info.plist for the framework that iOS will accept, when I try to run an app with one of the Firebase frameworks embedded, I get (sorry for non-codeblock spew, otherwise it's a single unreadable line):

Failure attempting to launch <XCUIApplicationImpl: 0x60400024d980 co.flightlabs.Flight at /Users/paul/Library/Developer/Xcode/DerivedData/Flight-cbyjdsglmnwngfasdbewusjszwnm/Build/Products/Debug-iphonesimulator/Flight.app>: Error Domain=IXUserPresentableErrorDomain Code=2 "This app was unable to be installed." UserInfo={NSLocalizedDescription=This app was unable to be installed., NSUnderlyingError=0x60400024ae90 {Error Domain=MIInstallerErrorDomain Code=35 "Failed to load Info.plist from bundle at path /Users/paul/Library/Developer/CoreSimulator/Devices/6530A98C-5983-447B-9972-052240711A00/data/Library/Caches/com.apple.mobile.installd.staging/temp.Jl6qEG/extracted/Flight.app/Frameworks/FirebaseCore.framework" UserInfo={LegacyErrorString=PackageInspectionFailed, FunctionName=-[MIBundle _validateWithError:], SourceFileLine=38, NSLocalizedDescription=Failed to load Info.plist from bundle at path /Users/paul/Library/Developer/CoreSimulator/Devices/6530A98C-5983-447B-9972-052240711A00/data/Library/Caches/com.apple.mobile.installd.staging/temp.Jl6qEG/extracted/Flight.app/Frameworks/FirebaseCore.framework}}}

[paulb777]

Thanks for the PR.

As discussed in #455, it's not clear that this is solving the issue.

Also, we're planning to remove the build.swift script with #444 since its original reason for existence (building drop in replacements of binary CocoaPod static frameworks) is going away. However, we're open to keeping it around if it addresses another use case.

[anaisbetts]

@paulb777 Ya, given build.swift is about to 🔥, no sense in this PR