[compiler.h] Migrate many C++ clients of countof to fbl::count_of

The latter is safer in C++, and the former is a namespace violation in
compiler.h that eventually needs to be resolved.

Test: CQ; should be no functional change
Change-Id: I9809b9fe062fd5f07226323035bf094b3f9de798

[syscalls] Remove count arguments from port_queue and port_wait

This argument is not used and always must be one. I tried implementing
some reasonable behavior for this parameter on port_queue, but it wasn't
clear what to do when we encounter an error during the queue operation
because there isn't an out parameter for how many we succeeded in
queuing.

Rather than having a half-baked feature, we should just remove the
parameter and add another function that does vectorized versions of
these operations if we need that in the future.

Change-Id: Ifffcd6d705442cc830912a67c8117ffe5ec8295d

[zx] Call zx_port_{wait,queue} with correct count

In the near future zx_port_{wait,queue} will not accept a count of zero.
Change all zircon callers to call these functions with a count of one.

ZX-1291 #comment

Change-Id: I5697208c7931a5e117f469c901c78f65615eeee0

[utest] Remove empty-string "msg" args from EXPECT/ASSERT calls in C++

The "msg" argument is optional in C++. A number of instances of
empty-string "msg" arguments have appeared since I last removed them.

This cleanup was automated.

ZX-905

Change-Id: I434d129836642216588f110d1cb161859ff3efea

[debugger] Remove out param for thread_read_state

The size of data being read and written should always be known in advance by
both caller and callee.

Removes backward-compatibility definitions from debug.h since the API is
currently changing in a non-backwards-compatible-way and we need to update
callers anyway. There were many changes associated with removing some users of
these structs and defines.

Add thread_read_state and thread_write_state to the zx::thread class.

Change-Id: I6d7e428d337f2722c529b68074dff16356984d63

[utest] Convert utest/debugger source to C++.

- Uses fbl atomics in place of C atomics.
- Remove now-unnecessary "struct" and "enum" specifiers.
- Replace some #defines with constexpr.
- Replace statics with an unnamed namespace.
- Add casts as necessary.
- Clang-format.

Change-Id: I707ccbec21ae7773933db0b1aea43798b12a7388