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/dev/native/cpp/main.cpp

@@ -4,11 +4,10 @@
 
 #include <iostream>
 
-#include "wpi/SmallVector.h"
-#include "wpi/StringRef.h"
+#include "wpi/SmallString.h"
 #include "wpi/hostname.h"
 
 int main() {
-  wpi::StringRef v1("Hello");
-  std::cout << v1.lower() << std::endl;
+  wpi::SmallString<128> v1("Hello");
+  std::cout << v1.str() << std::endl;
 }