Use native ruby plist serialization

For cross-platform consistency in execution output

Since Linux FSes have a tendency to be case-sensitive

Don't explicitly set ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES to NO

Read the correct SWIFT_VERSION when generating target XCConfigs

This reverts commit b6a874aa.

[CopyResourcesScript] add target_device 'tv' for tvOS

TARGETED_DEVICE_FAMILY will be 3) for tvOS.
Without this line we get the following error when running the '[CP] Copy Pods Resources' build phase on tvOS:

```
***-tvOS.storyboard: error: tvOS storyboards do not support target device type "mac".
```

[Validator] Strip newlines from .swift-version files