Use std::string_view and fmtlib across all libraries (#3402)

- Twine, StringRef, Format, and NativeFormatting have been removed
- Logging now uses fmtlib style formatting
- Nearly all uses of wpi::outs/errs have been replaced with fmt::print() or
std::puts()/std::fputs() (for unformatted strings).
- A wpi/fmt/raw_ostream.h header has been added to enable
fmt::print() with wpi::raw_ostream

wpiutil/src/main/native/cpp/Logger.cpp

@@ -0,0 +1,26 @@
+// 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/Logger.h"
+
+using namespace wpi;
+
+void Logger::DoLog(unsigned int level, const char* file, unsigned int line,
+                   const char* msg) {
+  if (!m_func || level < m_min_level) {
+    return;
+  }
+  m_func(level, file, line, msg);
+}
+
+void Logger::LogV(unsigned int level, const char* file, unsigned int line,
+                  fmt::string_view format, fmt::format_args args) {
+  if (!m_func || level < m_min_level) {
+    return;
+  }
+  fmt::memory_buffer out;
+  fmt::vformat_to(out, format, args);
+  out.push_back('\0');
+  m_func(level, file, line, out.data());
+}