[fdio][fidl] Use unaligned dirents for readdir, add ino

Test: fs-tests
ZX-2502 #done

Change-Id: I93e932a629f25c7da9f9a1a06e022d907ada47ed

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

Change-Id: Ie8d74e716da913bf6e2672c4acf8cd67b4962b7f

[minfs][blobfs] Re-implement filesystem teardown

Rather than simply "sync + exit process", implement
a fully featured filesystem teardown procedure, capable
of:
- Tearing down all active connections.
- Syncing underlying media using a non-blocking dispatch loop.
- Use closures to signal both mounters and unmounters on
filesystem destruction.

As a consequence of the controlled filesystem teardown
procedure, make the "filesystem" objects in minfs and blobfs
no longer refcounted, to clarify that "Shutdown" is the
single point of destruction after mounting.

ZX-1577 #done
ZX-1923 #done
ZX-1959 #done
ZX-1576 #comment In Progress

Change-Id: I3f8d71af76e391c41c665434baf86a245a7cd223

[blobfs] [minfs] [host] Combine common functionality between tools

De-dupe code between the minfs and blobfs host side tools as much as
possible. Additionally, add minfs support for adding manifests on create.

ZX-2033 #done

Change-Id: I0ece73d37927e6589ccd7d1ce235fc484668a221

[minfs] Convert minfs.h into private interface

Change-Id: I3a0fe542871172b591a0f178eb1d855f12742558

[minfs] [host] Fix memory leaks in host-side tool

ZX-1497 #done
ZX-1504 #done

Change-Id: Iffeeadca15706a05470a12c2a13b6dcf9ed772b8

[minfs] Only use O_PATH / O_DIRECTORY on host if they exist

Change-Id: I9a1c12103cb1e9a5905969e0747f91b16a73e469

[fs] Use the Fuchsia-defined open flags

Re-lands 2aff2cba029cf0f7e98e6d19f6dc7a663c318227

This change uses the Fuchsia-defined flags on the wire
as well as on filesystem servers. Clients interacting
with filesystems through the POSIX compatibility layer
can continue using POSIX open flags; they will be translated
by the RIO layers client-side.

ZX-1359 #comment In Progress

Change-Id: I4972c024547a0daa2146831e49e34d3ef905d4b4

[minfs] Refactor MinFS headers to be more fine-grained

Separate the following:
- On-Disk Structures
- Bcache (mechanism to interact with disk)
- MinFS Writeback
- MinFS Vnodes
- MinFS fsck

Into separate headers.

Change-Id: I920fe68d5c38ce53ed8e59ecee5003e6c3336577

[minfs] Convert MinFS to a library

ZX-1314 #comment In Progress

Change-Id: I0a7672d8321e0be07dd4c66232a0b4836db777a3