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/include/wpi/raw_istream.h

@@ -10,13 +10,12 @@
 #include <algorithm>
 #include <cstddef>
 #include <string>
+#include <string_view>
 #include <system_error>
 #include <vector>
 
 #include "wpi/ArrayRef.h"
 #include "wpi/SmallVector.h"
-#include "wpi/StringRef.h"
-#include "wpi/Twine.h"
 
 namespace wpi {
 
@@ -100,7 +99,7 @@ class raw_istream {
   // @param buf Buffer for output
   // @param maxLen Maximum length
   // @return Line
-  StringRef getline(SmallVectorImpl<char>& buf, int maxLen);
+  std::string_view getline(SmallVectorImpl<char>& buf, int maxLen);
 
   virtual void close() = 0;
 
@@ -154,7 +153,7 @@ class raw_mem_istream : public raw_istream {
 
 class raw_fd_istream : public raw_istream {
  public:
-  raw_fd_istream(const Twine& filename, std::error_code& ec,
+  raw_fd_istream(std::string_view filename, std::error_code& ec,
                  size_t bufSize = 4096);
   raw_fd_istream(int fd, bool shouldClose, size_t bufSize = 4096);
   ~raw_fd_istream() override;