[fdio] Simplify process args and protocol names

Now that we can recover the type of a socket from the kernel, we only
need one process arg id for passing pipes, stream, and datagram sockets.

Also, replace the duplicated FDIO_PROTOCOL_* definitions with their FIDL
equivalent.

Test: No behavior change

Change-Id: I8b4bd830b9ef836827be6060cd0c4e0c096a7bbc

[fd] Rename zxrio_object_info_t to zxrio_node_info_t

The new name matches the name in the FIDL protocol.

Test: No behavior change.
Change-Id: I742b72c2adbbaaf6aa16063edad7126a31d74bae

[fdio] Move headers into lib/fdio/...

Change-Id: Ie8d74e716da913bf6e2672c4acf8cd67b4962b7f

[blobstore] Rename blobstore to blobfs

Also, mount blobfs at /blob rather than /blobstore.

Change-Id: Ifdc473752ede37b909b30e35dbaac1397565a659