[kernel] Dispatchers and most kernel objects lockdep instrumented.

- Convert SoloDispatcher to a CRTP template type similar to
PeerDispatcher. This makes the lock classes for different solo
dispatchers distinct.
- Instrument the locks for all dispatchers.
- Instrument the locks for all kernel objects except those that
lock the thread_lock.

Bug: ZX-23
Test: k ut all and system/test/* pass + manual stress testing.

Change-Id: I8106c04911e47ea15ccce8e7abd5fbd62adfa6fe

[kernel] Move unittest.h to include/lib/unittest/

Move unittest.h deeper in the tree so include statements will say:

Change-Id: I85cb027a53530cd2003d813f004aaea3509f9f40

[kernel][unittest] Remove unused "void* context" argument from test cases

This argument is always NULL.

This argument was part of an init/cleanup feature that was unused and
that was removed.

Change-Id: I997a268be10c6837b2d7529fb92c2df2e3bab814

[kernel][unittest] Remove unused init/cleanup function parameters

None of the in-kernel test cases provide init or cleanup functions.
They all pass NULL to UNITTEST_END_TESTCASE() for those parameters, so
we can remove those parameters. Note that unittest.c wasn't actually
using the cleanup function.

Change-Id: I0332bc5c870deec8a021f543ec2c31ef95c30d0f

[dispatchers] Introduce peered dispatchers

Currently, several zircon dispatchers refer to their peers. These
include channels, sockets, fifos, and event pairs. These objects refer
both to their internal data as well as their signal state bits, as
well as their peers.

For a concrete example, consider zx_channel_write(h0, ...) on a
channel with endpoints h0 and h1. This of course modifies the message
packet buffer associated with h0. But it may also cause h1 to go from
unreadable to readable, so the signal state bits need to be updated.

Currently, this is accomplished by having separate data and signal
locks in the dispatchers, and taking them in a certain order. For the
channel write example, this is

1. h0 data lock
2. h1 data lock
a. h1 signal lock
b. h0 signal lock

where the indentation signifies scope (i.e. signal locks are taken
while holding signal locks.

For most other dispatcher kinds, the data and signal locks were
straightforwardly collapsed. The same approach (just having 1 lock and
not otherwise modifying locking call sites) does not work for peered
objects because of deadlock. The next easiest thing (dropping one
side's lock before taking the other) breaks the atomicity of the data
and signal updates.

Thus we introduce a method to share one lock between both ends of a
channel. The locking pattern for channel write changes to

1. h data lock
a. h1 signal lock
b. h0 signal lock

Subsequent CLs can then remove the per-peered-type signal locks, and
make it simply

1. h lock

When benchmarked, this approach reduced the zircon_benchmarks for
peered objects by reasonable amounts. For example, the
Channel/Write/64 bench went from about 650ns to 580ns on my NUC.

Change-Id: Ifb05ff75501cb2cea1bf0a506b6f647e788b47f3

[dispatcher][state_tracker] Move the state tracker into the dispatcher

Note that all access to the old StateTracker functionality is still
mediated by the has_state_tracker function. This is used to e.g. allow
only certain objects to be user signalled.

Change-Id: If9d0413eb131c6e7d70ea19c1ed928f7bf566cc8

[signals] Remove ZX_SIGNAL_LAST_HANDLE

Change-Id: I2ad0c145ea2c22ce022f9ab443fed24a3e3c7f65

[kernel][statetracker] Make OnCancel and OnCancelByKey take a const Handle*

Also mark one override of OnCancel as such.

Change-Id: Ic1fb0bebf490768848834db03a03a296321ff366

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[lib/magenta] Rename kernel/lib/magenta to kernel/object

TODO: Rename magenta.{cpp,h} and other instances of "magenta" in this
module.

For MG-1091 "Rename kernel/lib/magenta"

Change-Id: I2abc316f543798e00d3a4d1c2c83195da26e6836