[sysid] Add SysId (#5672)

The source is copied from this commit:
625ff04784.

sysid/src/main/native/cpp/view/JSONConverter.cpp

@@ -0,0 +1,64 @@
+// 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/analysis/JSONConverter.h"
+#include "sysid/view/JSONConverter.h"
+
+#include <exception>
+
+#include <imgui.h>
+#include <portable-file-dialogs.h>
+#include <wpi/timestamp.h>
+
+#include "sysid/Util.h"
+
+using namespace sysid;
+
+void JSONConverter::DisplayConverter(
+    const char* tooltip,
+    std::function<std::string(std::string_view, wpi::Logger&)> converter) {
+  if (ImGui::Button(tooltip)) {
+    m_opener = std::make_unique<pfd::open_file>(
+        tooltip, "", std::vector<std::string>{"JSON File", SYSID_PFD_JSON_EXT});
+  }
+
+  if (m_opener && m_opener->ready()) {
+    if (!m_opener->result().empty()) {
+      m_location = m_opener->result()[0];
+      try {
+        converter(m_location, m_logger);
+        m_timestamp = wpi::Now() * 1E-6;
+      } catch (const std::exception& e) {
+        ImGui::OpenPopup("Exception Caught!");
+        m_exception = e.what();
+      }
+    }
+    m_opener.reset();
+  }
+
+  if (wpi::Now() * 1E-6 - m_timestamp < 5) {
+    ImGui::SameLine();
+    ImGui::Text("Saved!");
+  }
+
+  // Handle exceptions.
+  ImGui::SetNextWindowSize(ImVec2(480.f, 0.0f));
+  if (ImGui::BeginPopupModal("Exception Caught!")) {
+    ImGui::PushTextWrapPos(0.0f);
+    ImGui::Text(
+        "An error occurred when parsing the JSON. This most likely means that "
+        "the JSON data is incorrectly formatted.");
+    ImGui::TextColored(ImVec4(1.0f, 0.4f, 0.4f, 1.0f), "%s",
+                       m_exception.c_str());
+    ImGui::PopTextWrapPos();
+    if (ImGui::Button("Close")) {
+      ImGui::CloseCurrentPopup();
+    }
+    ImGui::EndPopup();
+  }
+}
+
+void JSONConverter::DisplayCSVConvert() {
+  DisplayConverter("Select SysId JSON", sysid::ToCSV);
+}