chore: move mfs and multipart files into core

[achingbrain]

I've converted the mfs tests to interface tests and they are a lot more thorough than the previous ones.

Turns out a whole bunch of stuff didn't work over http. Also, some of our interface tests now make go-ipfs fail, mostly around mfs operations on hamt shards - removing files from shards in particular. I've skipped all of these tests when we run against go-ipfs but we'll need some follow up issues.

BREAKING CHANGES:

ipfs.files.stat(path) run on a hamt sharded directory used to report a type of hamt-sharded-directory, now it reports directory to bring js-ipfs in line with go-ipfs.

[hugomrdias]

can you explain why we need this ?

[achingbrain]

If the body is a stream, and that stream errors the error is not surfaced to the calling code.

This will throw any error thrown until the response headers arrive. I'm not sure if we should keep it TBH as it stops working once the response headers have been received, after that any error is smothered, same as without the bodyErr lines in the PR.

It makes this test pass (http://localhost:3000 is an echo server):

it('should handle errors in streaming bodies', async function () {
  const err = new Error('Should be caught')
  const body = async function * () {
    yield Buffer.from([0, 1, 2])

    // await delay(1000) <-- uncomment this line and the test fails as the 
    // response headers arrive before err is thrown

    throw err
  }()

  await expect(HTTP.post('http://localhost:3000', {
    body: toStream.readable(body)
  })).to.eventually.be.rejectedWith(err)
})