Add a boxing utility which can surround a bunch of UI and render it in a box.

The ImGui table API cell padding variables can be used to adjust the positioning of the UI in the box.

PiperOrigin-RevId: 858137824
Change-Id: I1ce1519c0abd67bc5fafc30f9a18dfcf18c2a313

src/experimental/platform/imgui_widgets.h

@@ -265,6 +265,19 @@ inline bool ImGui_IsChordJustPressed(ImGuiKeyChord chord) {
   return ImGui::IsKeyChordPressed(chord, 0);
 }
 
+// Begin a boxed section with outer borders - use EndBoxSection to close.
+inline bool BeginBoxSection(const char* id, ImGuiTableFlags extra_flags = 0) {
+  ImGuiTableFlags flags = ImGuiTableFlags_BordersOuter | extra_flags;
+  if (ImGui::BeginTable(id, 1, flags)) {
+    ImGui::TableNextRow();
+    ImGui::TableNextColumn();
+    return true;
+  }
+  return false;
+}
+
+inline void EndBoxSection() { ImGui::EndTable(); }
+
 // Saves the given contents to the clipboard if the clipboard is available.
 void MaybeSaveToClipboard(const std::string& contents);