Add support for stream based encryption

This is really just experimentation so far. Let's first discuss things actually.

@todo Update the issue summary so it makes more sense actually

I'll working on summarizing what we discussed in IRC.

After looking into defuse for a while, I think their way is the way to go

• Its as simple as you can get
• It supports any kind of resource, so both file and simply memory could be used
• Even remote resources, aka. any kind of stream wrapper is supported
• By using resources the actual encryption library (defuse) can choose to do things in an actual streaming way

Let's come up with the interface which could make sense here:

interface EncryptStreamInterface {
  public function encrypt($input_handler, $output_handle, EncryptionProfileInterface $encryption_profile);
  public function decrypt($input_handler, $output_handle, EncryptionProfileInterface $encryption_profile);
}

The simplest implementation for this interface is to actually read in the entire stream, decrypt/encrypt it, and write it back. This is provided in NoStreaming and is proven to work, at least on the file_encrypt tests.

Integration with external libraries (defuse / halite)

In order for them to integrate into that architecture we would need some way for encryption methods to provide a special streaming class.
A suggestion to do so (not yet in the patch):

• Provide a stream_class which can be used to create a streaming implementation
• When the encryption method doesn't provide one, fall back to NoStreaming which should always work

Potential halite implementation

ParagonIE\Halite\File::encrypt and ParagonIE\Halite\File::decrypt both provide a way to pass in a resource, so the stream implementation would just hae to be able to extract the actual halite key output of the encryption profile, which should be doable.

Potential defuse implementation

Defuse\Crypt\File::encryptResource and Defuse\Crypt\File:decryptResource has a similar signature to halite, so again, the only trick we need is to extract the right key object.

File_encrypt Implementation

More on https://github.com/d8-contrib-modules/file_encrypt/issues/5

Here is some form of simple patch, not yet with the swappability included.

Here is a method on the encryption method which allows you to retrieve the stream implementation. This seems to work basically how you expect it to work like.

I guess the next step is to implement it actually for halite or defuse to prove its what we need. Another step would be to encrypt a gigantic file and check how much memory is used in memory for that. Currently the fact that we use a memory stream in \Drupal\file_encrypt\EncryptStreamWrapper::stream_close seems to make that bit impossible. Let's see how things turn out in the future ... but this seems to be totally a file_encrypt problem now ... hopefully ...