[XCConfig] Only include -ObjC flag when linking against a static lib

[Validator] Disable default plugins when installing

[EmbedFrameworksScript] Quote all the things

[Installer] Add support for default plugins

[Installer] Save the Pods project with deterministic UUIDs

Public headers in a directory named `framework` should be linked in the sandbox

[Downloader] Run prepare_command even when skipping the cache

[Resolver] Take supported platforms into account when resolving