C++17ification.

C++17ification!

- Filesystem interaction now uses std::filesystem::path.
- Usage of const char*, std::string have been changed to
  std::string_view where appropriate.
- Usage of printf-style functions changed to use fmt.

src/xenia/apu/xma_decoder.cc

@@ -91,7 +91,7 @@ void av_log_callback(void* avcl, int level, const char* fmt, va_list va) {
 
   StringBuffer buff;
   buff.AppendVarargs(fmt, va);
-  xe::LogLineFormat(log_level, level_char, "libav: %s", buff.GetString());
+  xe::LogLineFormat(log_level, level_char, "libav: %s", buff.buffer());
 }
 
 X_STATUS XmaDecoder::Setup(kernel::KernelState* kernel_state) {