[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.

Bug: ZX-905
Test: compile
Change-Id: Ia5ef96a2bc5a91dd8d1d62c90802c26f44f1a31f

[syslog] Add fallback mode support.

This mode will be used when logger fidl service crashes or fails to
process messages. This mode can also be used for specific errors with
socket writes.

Change-Id: I02ab21725d590a1f9632a153ca9d00275057913c

[zx] Move public zx headers to match naming convention

The zx library provides headers intended for general use, so the
include path should be spelled <lib/zx/foo.h> as per
https://fuchsia.googlesource.com/docs/+/master/development/languages/c-cpp/naming.md.
This moves the headers into the proper location and updates includes to
match.

Change-Id: I6fc9b2a491b5f8b0d270c4dfc77fa4be5739071b

[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

[syslog] Remove DEBUG level from syslogger

Change-Id: I8d60bbf4f08d71f64751f5afe97ff37e37eb08ee

[unittest] Remove 'length' argument from EXPECT_STR_EQ()/ASSERT_STR_EQ()

The 'length' argument is redundant now that these two functions always
compare the whole strings.

I updated the call sites using an automated tool.

I've removed the now-unneeded EXPECT_STRING_EQ() wrapper in
syslog_socket_tests.cpp.

Change-Id: I80fff5c5ccdc44337125bc2b2d3386fc6606f1dc

[unittest] Make EXPECT/ASSERT_STR_EQ() stricter: always compare whole strings

Before this change, EXPECT_STR_EQ(X,Y,N) and ASSERT_STR_EQ(X,Y,N)
don't actually compare the strings X and Y for equality -- they only
compare the first N characters, using strncmp(). That is inconvenient
and weird, and unexpected given their names.

Address this by making them stricter so that they always compare the
whole strings. This works for all the call sites except one, where a
non-null-terminated string was being checked, for which we can use
ASSERT_BYTES_EQ() instead.

In a follow-on change we can remove the 'length' argument.

Change-Id: I138aea151cc5e1eb68e8afdb333b3e0eabd54dd2

[syslog] No longer attempt to format raw messages.

FX_LOG() and fx_log() no longer attempt to format message strings.

Do not pass those message through printf as they are preprocessed.

Change-Id: Ie9b784859ca64fe31d2ab6e1747bf83f31d0016e

[syslog] Add macros for verbosity

Change-Id: I6fd91b555541a820b878b8ef06788b29f4d99bfb

[syslog] Format code

Formatting using //script/git-file-format

Change-Id: I6f572735d2ee510ebf0348db34916656974f365c

[syslog] Add support for writing to socket

ZX-1665

Change-Id: Ie21550b6784deeebc4ed8b752534108dfcbd1640