[sysid] Add SysId (#5672)

The source is copied from this commit:
625ff04784.

sysid/src/main/native/cpp/Util.cpp

@@ -0,0 +1,80 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "sysid/Util.h"
+
+#include <filesystem>
+#include <stdexcept>
+
+#include <imgui.h>
+#include <wpi/raw_ostream.h>
+
+void sysid::CreateTooltip(const char* text) {
+  ImGui::SameLine();
+  ImGui::TextDisabled(" (?)");
+
+  if (ImGui::IsItemHovered()) {
+    ImGui::BeginTooltip();
+    ImGui::PushTextWrapPos(ImGui::GetFontSize() * 35.0f);
+    ImGui::TextUnformatted(text);
+    ImGui::PopTextWrapPos();
+    ImGui::EndTooltip();
+  }
+}
+
+void sysid::CreateErrorPopup(bool& isError, std::string_view errorMessage) {
+  if (isError) {
+    ImGui::OpenPopup("Exception Caught!");
+  }
+
+  // Handle exceptions.
+  ImGui::SetNextWindowSize(ImVec2(480.f, 0.0f));
+  if (ImGui::BeginPopupModal("Exception Caught!")) {
+    ImGui::PushTextWrapPos(0.0f);
+    ImGui::TextColored(ImVec4(1.0f, 0.4f, 0.4f, 1.0f), "%s",
+                       errorMessage.data());
+    ImGui::PopTextWrapPos();
+    if (ImGui::Button("Close")) {
+      ImGui::CloseCurrentPopup();
+      isError = false;
+    }
+    ImGui::EndPopup();
+  }
+}
+
+std::string_view sysid::GetAbbreviation(std::string_view unit) {
+  if (unit == "Meters") {
+    return "m";
+  } else if (unit == "Feet") {
+    return "ft";
+  } else if (unit == "Inches") {
+    return "in";
+  } else if (unit == "Radians") {
+    return "rad";
+  } else if (unit == "Degrees") {
+    return "deg";
+  } else if (unit == "Rotations") {
+    return "rot";
+  } else {
+    throw std::runtime_error("Invalid Unit");
+  }
+}
+
+void sysid::SaveFile(std::string_view contents,
+                     const std::filesystem::path& path) {
+  // Create the path if it doesn't already exist.
+  std::filesystem::create_directories(path.root_directory());
+
+  // Open a fd_ostream to write to file.
+  std::error_code ec;
+  wpi::raw_fd_ostream ostream{path.string(), ec};
+
+  // Check error code.
+  if (ec) {
+    throw std::runtime_error("Cannot write to file: " + ec.message());
+  }
+
+  // Write contents.
+  ostream << contents;
+}