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/examples/usbviewer/usbviewer.cpp

@@ -6,12 +6,13 @@
 #include <thread>
 #include <vector>
 
+#include <fmt/format.h>
+
 #define IMGUI_DEFINE_MATH_OPERATORS
 #include <imgui.h>
 #include <imgui_internal.h>
 #include <opencv2/core/core.hpp>
 #include <opencv2/imgproc.hpp>
-#include <wpi/raw_ostream.h>
 #include <wpi/spinlock.h>
 #include <wpigui.h>
 
@@ -38,7 +39,7 @@ int main() {
       // get frame from camera
       uint64_t time = cvsink.GrabFrame(frame);
       if (time == 0) {
-        wpi::outs() << "error: " << cvsink.GetError() << '\n';
+        fmt::print("error: {}\n", cvsink.GetError());
         continue;
       }