[wpiutil] Split DataLog background writer into different class (#6590)

DataLog is now a base class, with DataLogBackgroundWriter being the
background thread version and DataLogWriter being a non-threaded version.

Also split the C header into a separate file to make it more wpiformat friendly.

wpiutil/src/main/native/cpp/DataLogWriter.cpp

@@ -0,0 +1,76 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "wpi/DataLogWriter.h"
+
+#include "wpi/raw_ostream.h"
+
+using namespace wpi::log;
+
+DataLogWriter::DataLogWriter(std::string_view filename, std::error_code& ec,
+                             std::string_view extraHeader)
+    : DataLogWriter{s_defaultMessageLog, filename, ec, extraHeader} {}
+
+DataLogWriter::DataLogWriter(wpi::Logger& msglog, std::string_view filename,
+                             std::error_code& ec, std::string_view extraHeader)
+    : DataLogWriter{msglog, std::make_unique<raw_fd_ostream>(filename, ec),
+                    extraHeader} {
+  if (ec) {
+    Stop();
+  }
+}
+
+DataLogWriter::DataLogWriter(std::unique_ptr<wpi::raw_ostream> os,
+                             std::string_view extraHeader)
+    : DataLogWriter{s_defaultMessageLog, std::move(os), extraHeader} {}
+
+DataLogWriter::DataLogWriter(wpi::Logger& msglog,
+                             std::unique_ptr<wpi::raw_ostream> os,
+                             std::string_view extraHeader)
+    : DataLog{msglog, extraHeader}, m_os{std::move(os)} {
+  StartFile();
+}
+
+DataLogWriter::~DataLogWriter() {
+  if (m_os) {
+    Flush();
+  }
+}
+
+void DataLogWriter::Flush() {
+  if (!m_os) {
+    return;
+  }
+  std::vector<Buffer> writeBufs;
+  FlushBufs(&writeBufs);
+  for (auto&& buf : writeBufs) {
+    (*m_os) << buf.GetData();
+  }
+  ReleaseBufs(&writeBufs);
+}
+
+void DataLogWriter::Stop() {
+  DataLog::Stop();
+  Flush();
+  m_os.reset();
+}
+
+bool DataLogWriter::BufferFull() {
+  Flush();
+  return false;
+}
+
+extern "C" {
+
+struct WPI_DataLog* WPI_DataLog_CreateWriter(const char* filename,
+                                             int* errorCode,
+                                             const char* extraHeader) {
+  std::error_code ec;
+  auto rv = reinterpret_cast<WPI_DataLog*>(
+      new DataLogWriter{filename, ec, extraHeader});
+  *errorCode = ec.value();
+  return rv;
+}
+
+}  // extern "C"