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

glass/src/lib/native/cpp/other/Mechanism2D.cpp

@@ -6,9 +6,12 @@
 
 #include <algorithm>
 #include <cmath>
+#include <cstdio>
 #include <memory>
+#include <string_view>
 #include <utility>
 
+#include <fmt/format.h>
 #include <frc/geometry/Pose2d.h>
 #include <frc/geometry/Rotation2d.h>
 #include <frc/geometry/Transform2d.h>
@@ -21,7 +24,6 @@
 #include <portable-file-dialogs.h>
 #include <units/angle.h>
 #include <units/length.h>
-#include <wpi/raw_ostream.h>
 #include <wpigui.h>
 
 #include "glass/Context.h"
@@ -125,10 +127,10 @@ void BackgroundInfo::LoadImage() {
 }
 
 bool BackgroundInfo::LoadImageImpl(const char* fn) {
-  wpi::outs() << "GUI: loading background image '" << fn << "'\n";
+  fmt::print("GUI: loading background image '{}'\n", fn);
   auto texture = gui::Texture::CreateFromFile(fn);
   if (!texture) {
-    wpi::errs() << "GUI: could not read background image\n";
+    std::puts("GUI: could not read background image");
     return false;
   }
   m_texture = std::move(texture);
@@ -182,7 +184,7 @@ void glass::DisplayMechanism2DSettings(Mechanism2DModel* model) {
 void FrameData::DrawObject(ImDrawList* drawList, MechanismObjectModel& objModel,
                            const frc::Pose2d& pose) const {
   const char* type = objModel.GetType();
-  if (wpi::StringRef{type} == "line") {
+  if (std::string_view{type} == "line") {
     auto startPose =
         pose + frc::Transform2d{frc::Translation2d{}, objModel.GetAngle()};
     auto endPose =