CLogger: Use cppformat instead of sys_vswprintf.

sys_vswprintf relies on platform-specific printf implementations, which
vary widely between platforms (in handling of truncation, return values,
use of %s/%S/%hs/%ls for mixing char and wchar_t strings, etc) and are
therefore a pain.

Use cppformat's fmt::sprintf instead, which has very similar syntax to
sprintf but is more C++ish and is portable.

Also, wchar_t is stupid, so use char* strings (which are expected to be
UTF-8) in CLogger. This creates a bit of a pain with changing all
callers to convert to char* strings, but that's their fault for not
using UTF-8 already.

Refs #3011.

This was SVN commit r16182.

source/test_setup.cpp

@@ -100,6 +100,11 @@ static MiscSetup miscSetup;
 
 // Definition of functions from lib/self_test.h
 
+bool ts_str_contains(const std::string& str1, const std::string& str2)
+{
+	return str1.find(str2) != str1.npos;
+}
+
 bool ts_str_contains(const std::wstring& str1, const std::wstring& str2)
 {
 	return str1.find(str2) != str1.npos;