[syscalls] Change vmar_... calls

- Create zx_vm_option_t type
- Change ZX_VM_FLAG_... to ZX_VM_... and make them new type.
- Change int32_t flags parameters to zx_vm_option_t options
- Make the options parameter be second.

- Modify vmar_..._old functions to keep other repos working.
Once they've all been updated these functions will go away.

ZX-2264
Test:CQ

Change-Id: I1faf4cc4e1e4dabf3d8ef680e398d83a545b0f09

[zircon] Add ZX_VMO_ZERO_CHILDREN signal

This CL wires a new signal to VMO, which starts asserted
and de-asserts when a given VMO has live children, normally
associated with child COW clones.

This enables a more efficient filesystem server

ZX-1758 #comment progress

Change-Id: If5aca34cba7a699469e931491cb97aa3ffb0794f

[signals] Remove ZX_SIGNAL_LAST_HANDLE

Change-Id: I2ad0c145ea2c22ce022f9ab443fed24a3e3c7f65

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[unittest] Use ASSERT_NE()/EXPECT_NE() instead of ASSERT_NEQ()/EXPECT_NEQ()

This is to make the interface more consistent with gtest, which uses
the _NE suffix rather than _NEQ for "not equal".

Change-Id: Ic03fda7322ab79cbd806c8f849b6956d201c6d45

[utest][handles] don't treat handles as signed

Otherwise we can't build when they become unsigned.

Change-Id: I9af3e25c9716a41985320016c5559c09d6c8e520

[utest][core] MX_ERR_-ify the core unit tests

Change-Id: Iebfbeba437831ad4b85d1b0bc6d6dc22bb721de9

[kernel][magenta] last handle signal

Introduces a new signal MX_SIGNAL_LAST_HANDLE which
is on by default on new created objects.

Moves all the heavy logic of 0 handle, one handle
and so on to magenta.cpp which is already taking
the very convenient lock. This also removes
the atomic operations on the handle count, however
in order to properly synchronize the handle
count and the signals, a fairly ugly
double check is introduced in the state_tracker
via StateTracker::UpdateLastHandleSignal()

- Adds a new .md that better explains generic signals
- Adds new tests for the corner cases.

The rest of the code is fixing the many tests
that compare signals with a particular value which
need to be updated for the new signal that
shows up unless the handle is duplicated.

Change-Id: Id42b3fe951c16407bc08e18bb342ddd8f2830bf9

[time] Switch callers of syscalls with timeouts to use conversion function

This is in preparation for moving syscalls to absolute deadlines rather
than relative timeouts.

Change-Id: Ic85abbf76f34fbce7899c2505be840e3d3dcf7ff

[syscalls] update callers to mx_handle_wait_*() and deprecate

Change-Id: I7b0516007b99d58aee906eac62358625100ee32e

[kernel][magenta] Add support for user signals on VMO handles

Change-Id: I3a8611e3e55179cede1598d7911bbcc7528d44c3