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

cscore/src/main/native/cpp/Instance.cpp

@@ -4,36 +4,32 @@
 
 #include "Instance.h"
 
-#include <wpi/SmallString.h>
-#include <wpi/StringRef.h>
+#include <string_view>
+
+#include <fmt/format.h>
 #include <wpi/fs.h>
-#include <wpi/raw_ostream.h>
 
 using namespace cs;
 
 static void def_log_func(unsigned int level, const char* file,
                          unsigned int line, const char* msg) {
-  wpi::SmallString<128> buf;
-  wpi::raw_svector_ostream oss(buf);
   if (level == 20) {
-    oss << "CS: " << msg << '\n';
-    wpi::errs() << oss.str();
+    fmt::print(stderr, "CS: {}\n", msg);
     return;
   }
 
-  wpi::StringRef levelmsg;
+  std::string_view levelmsg;
   if (level >= 50) {
-    levelmsg = "CRITICAL: ";
+    levelmsg = "CRITICAL";
   } else if (level >= 40) {
-    levelmsg = "ERROR: ";
+    levelmsg = "ERROR";
   } else if (level >= 30) {
-    levelmsg = "WARNING: ";
+    levelmsg = "WARNING";
   } else {
     return;
   }
-  oss << "CS: " << levelmsg << msg << " (" << fs::path{file}.filename().string()
-      << ':' << line << ")\n";
-  wpi::errs() << oss.str();
+  fmt::print(stderr, "CS: {}: {} ({}:{})\n", levelmsg, msg,
+             fs::path{file}.filename().string(), line);
 }
 
 Instance::Instance()