[vmo-utils][fzl] Move contents of vmo-utils into fzl

Move copies of the vmo-centric helper classes which existed in
vmo-utils into fzl. This is step one of merging vmo-utils and libfzl.
Once higher level code has been migrated over to use the new library,
vmo-utils and its tests can be removed.

Also, merge the libfzl and fzl unit tests. I'm not sure how they got
divided in the first place, but now they are unified under just
libfzl.

ZX-2462 #comment Classes have been duplicated and added to libfzl
Test: Build and unit-test

Change-Id: Ie3bc07a9f78b6383032fcc974f28dd6af50caf21

[zx][fzl] Implement ticks class, fzl helper library.

This patch:
- Implements the zx::ticks class, wrapping zx_ticks_t
- Implements the fzl library, which provides a C and C++ API
for converting between nanoseconds and ticks. Since libzx is
intended to act purely as a C++ wrapper class around the underlying
C API, fzl contains "more-complex-than-just-syscall" logic for general
Zircon-specific system helpers.
- Tests both changes.

Change-Id: I089e3cd64b780042d1cb7a48e455a10e21b2cf20