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When we close a connection, we set the "stream" set to nil to avoid opening new
stream. Unfortunately, this meant we wouldn't decrement the reference count on
the swarm.

This commit switches over to the new Close/CloseWrite/CloseRead interface
changes in go-libp2p-core 0.7.0.

This change also removes a now obsolete hack to implicitly clean up streams
after reading an EOF; calling Close or Reset is now required.

See: https://github.com/libp2p/go-libp2p-core/releases/tag/v0.7.0

Co-authored-by: Aarsh Shah <aarshkshah1992@gmail.com>
Co-authored-by: Raúl Kripalani <raul@protocol.ai>

If they don't, this could end up reading a bunch of internal data, causing a
race (and yes, this has happened).

This reverts commit 3dded3dc.

Removes:

* go-libp2p-conn logic (moved to transports)
* go-libp2p-peerstream (moved here)

Changes:

* New transport interface.
* Explicit over implicit (the implicit automagic now all lives in go-libp2p):
  * No more default transports, muxers, etc.
  * No more fallback dialer. Transports are now *required*.
* Stream opening:
  * Connection picking logic (instead of just picking the first).
  * Tries harder to open a stream of some connections happen to be closed.
* Stream closing:
  * No longer treats half-closed streams as fully closed. Users *must* read the
    an EOF or reset the stream for it to be garbage collected.
* No more polling for dead connections.
* Multiplexers are now *non-optional*. Really, they haven't been optional for a
  while but we still pretended that they were.
* No more Network type alias. It added a bunch of code and didn't really provide
  anything but an alternative set of methods that do the same thing.
* Notifications:
  * New guarantee: connection open notifications will complete before connection
    close notifications begin.
  * Given that, notifications are now delivered in parallel. No more
    notification backlogs blocking connection closing/opening.

We already setup the connection from within the new connection handler. No need
to do it *again* on dial.