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

wpilibc/src/main/native/cpp/Relay.cpp

@@ -178,7 +178,7 @@ void Relay::InitSendable(SendableBuilder& builder) {
   builder.SetSafeState([=]() { Set(kOff); });
   builder.AddSmallStringProperty(
       "Value",
-      [=](wpi::SmallVectorImpl<char>& buf) -> wpi::StringRef {
+      [=](wpi::SmallVectorImpl<char>& buf) -> std::string_view {
         switch (Get()) {
           case kOn:
             return "On";
@@ -190,7 +190,7 @@ void Relay::InitSendable(SendableBuilder& builder) {
             return "Off";
         }
       },
-      [=](wpi::StringRef value) {
+      [=](std::string_view value) {
         if (value == "Off") {
           Set(kOff);
         } else if (value == "Forward") {