add explicit conformances to Array.DifferentiableView

[marcrasi]

This fixes some errors caused by swiftlang/swift#27971:

/home/swiftci/jenkins/workspace/swift-PR-TensorFlow-Linux-gpu/tensorflow-swift-apis/Sources/TensorFlow/StdlibExtensions.swift:196:1: error: conditional conformance of type 'Array<Element>.DifferentiableView' to protocol 'MutableCollection' does not imply conformance to inherited protocol 'Collection'
extension Array.DifferentiableView
^
/home/swiftci/jenkins/workspace/swift-PR-TensorFlow-Linux-gpu/tensorflow-swift-apis/Sources/TensorFlow/StdlibExtensions.swift:196:1: error: conditional conformance of type 'Array<Element>.DifferentiableView' to protocol 'RandomAccessCollection' does not imply conformance to inherited protocol 'BidirectionalCollection'
extension Array.DifferentiableView
^
/home/swiftci/jenkins/workspace/swift-PR-TensorFlow-Linux-gpu/tensorflow-swift-apis/Sources/TensorFlow/StdlibExtensions.swift:196:1: error: conditional conformance of type 'Array<Element>.DifferentiableView' to protocol 'MutableCollection' does not imply conformance to inherited protocol 'Sequence'
extension Array.DifferentiableView
^
/home/swiftci/jenkins/workspace/swift-PR-TensorFlow-Linux-gpu/tensorflow-swift-apis/Sources/TensorFlow/StdlibExtensions.swift:196:1: note: did you mean to explicitly state the conformance like 'extension DifferentiableView: Sequence where ...'?
extension Array.DifferentiableView
^