Refactor CMake configuration for ImGuiTestEngine and feature flags

- Updated the CMake configuration to use target_compile_definitions for ImGuiTestEngine, improving clarity and maintainability.
- Introduced IMGUI_TEST_ENGINE_DEFINITIONS to streamline the definition process for targets linking to ImGuiTestEngine.
- Modified feature flags in features.h to conditionally enable the native file dialog based on the YAZE_ENABLE_NFD flag, enhancing flexibility in feature management.

src/app/gui/input.cc

@@ -240,7 +240,7 @@ void ItemLabel(absl::string_view title, ItemLabelFlags flags) {
   const ImGuiStyle& style = ImGui::GetStyle();
   float fullWidth = ImGui::GetContentRegionAvail().x;
   float itemWidth = ImGui::CalcItemWidth() + style.ItemSpacing.x;
-  ImVec2 textSize = ImGui::CalcTextSize(title.begin(), title.end());
+  ImVec2 textSize = ImGui::CalcTextSize(title.data(), title.data() + title.size());
   ImRect textRect;
   textRect.Min = ImGui::GetCursorScreenPos();
   if (flags & ItemLabelFlag::Right) textRect.Min.x = textRect.Min.x + itemWidth;