[sync] Apply C API rubric to libsync

Test: No behavior change
Change-Id: I30a413f7fb5d3f4e741e5204532b82e73595c086

[block-client] Add RAII C++ wrapper around block client

Test: fs, ramdisk, blobfs, fvm
ZX-2123 #done

Change-Id: I1f0d9eca48939c5c874fe5a6a9721e309e4eb338

[block] Implement v2 of Block Protocol

- "Transactions" renamed to "Groups". The term
transaction remains, and is used to corresponds to a
single FIFO request.
- "Groups" pre-allocated by block server.
Clients can use groups between [0, MAX_TXN_GROUP_COUNT)
without needing to allocate. Groups signify structures
that can wait to transmit responses for a collection of
transactions. These transactions may be requested via
"BLOCKIO_TXN_GROUP"; the block-client library does this
automatically.
- "One-shot" transactions, which are not associated with
a group, are also implemented. All "one-shot" transactions
receive a FIFO response.

ZX-1584 #done
ZX-1580 #comment In Progress

TEST=ramdisk, fvm, zxcrypt, block, fs tests, running iochk manually

Change-Id: I7caf342804baf32543adfef3fec76f7d77d89b3f

[fifo] zx_fifo_read/write bytes->elems migration, part 4.1

Switch callers of zx_fifo_{read,write} to new calls.
This doesn't include the C++ wrappers and their callers yet.

ZX-1951

Change-Id: I9e61a50f945d3a91cddf8e5f0ec852297d6e5770

[fifo] zx_fifo_read/write bytes->entries migration, part 1

- Introduce zx_fifo_read_old and zx_fifo_write_old
- Mark zx_fifo_read and zx_fifo_write as deprecated
- Migrate all callers in zircon to the "_old" versions

ZX-1951 #comment

Change-Id: I3be0ace412a6fe9d729eaf9a581bbf88cd45effe

[block] Add queueing to block midlayer.

Additionally, implement sync barriers within the block midlayer.

ZX-1582 #done
ZX-1584 #comment In Progress

Change-Id: Id6c084d13ffa91ededab7d5f731614f81ccf1b2b

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[ulib][status] Use the MX_OK and MX_ERR_* mx_status_t names

Change-Id: I3ba531de766b559b8922fb4910715c630efc9b82

[magenta][errors] Rename ERR_REMOTE_CLOSED to ERR_PEER_CLOSED

This error, at least at the Magenta syscall level, is really about
peers. This new name aligns with the MX_*_PEER_CLOSED signals. And
REMOTE implies a distance or asymmetry that isn't necessarily true.

This leaves a compatibility alias for the old name in place until the
rest of Fuchsia can be cleaned up.

Change-Id: Icf95003b2813270d865c6876b62e21d9f5b8c0f6

[block][ramdisk] Add FIFO support to block device

- Implemented ulib/block library to support FIFO-based block
protocol.
- Added "udev/block", acting as a global block device. Added
MX_PROTOCOL_BLOCK_CORE, which will be implemented by all
"hardware-specific" block devices. "udev/block" binds
to any hardware-specific devies that implement this protocol.
udev/block calls into the ulib/block library, which deals
with the client / server interaction.
- Updated utest/ramdisk to test the ulib/block protocol.
- Updated all uses of opening the ramdisk, so it can be accessed
through the superset of the udev/block interface.

Change-Id: I85d4d1ba70eed5c2b0bdcfbe5ff23d88afcd60cf