Avoid multiple allocations in BlobModule

[JunielKatarn]

See https://github.com/microsoft/react-native-windows/pull/6079/files/359f9c92e0143b89d3d40efa1a2ad54c06871bf0#r494023291

Type std::vector<std::uint8_t> is used to both store and expose binary data by WebSocketModule.
When the blob type is used, and a segment projection is required (see IWebSocketContentHandler::ResolveMessage), a new vector object is created, copying the immutable data over.

Find a way to create this "slice" vector without copying, but also without modifying interface signatures in IWebSocketResource, or determine the proper storage/transfer type for binary data.
This should accommodate both blob and arrayBuffer binary types.

[chrisglein]

We don’t officially support BlobModule yet, and it is not a 0.64 target feature. Moving this out.