Link the texture displacement guide and wiki from the gizmo panel

Finding either piece of documentation currently means knowing it exists and
going looking for it outside the application, which is the hardest moment to
do that: the panel has a lot of controls and the feature is new.

Add two borderless icon buttons to the panel header, next to the dock toggle,
opening the video walkthrough and the wiki page in the default browser. Both
icons follow the set's existing convention of a grey outline with a teal
accent, so they read as part of the same panel.

resources/images/texture_displacement_video_guide.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><rect x="0.5" y="2.5" width="15" height="11" rx="2.5" style="fill:none;stroke:#949494;stroke-linecap:round;stroke-linejoin:round"/><path d="M6.5 5.5l4.5 2.5-4.5 2.5z" style="fill:none;stroke:#009688;stroke-linecap:round;stroke-linejoin:round"/></svg>

resources/images/texture_displacement_wiki.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" viewBox="0 0 16 16"><path d="M1.5 2.5h4a2 2 0 0 1 2 2v9a1.5 1.5 0 0 0-1.5-1.5h-4.5zM14.5 2.5h-4a2 2 0 0 0-2 2v9a1.5 1.5 0 0 1 1.5-1.5h4.5z" style="fill:none;stroke:#949494;stroke-linecap:round;stroke-linejoin:round"/><path d="M10.5 5.5h2.5M10.5 7.5h2.5M3 5.5h2.5M3 7.5h2.5" style="fill:none;stroke:#009688;stroke-linecap:round;stroke-linejoin:round"/></svg>

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.cpp

@@ -3362,6 +3362,8 @@ void GLGizmoTextureDisplacement::ensure_panel_icons()
         "texture_displacement_adjust.svg", "canvas_drag.svg", "texture_displacement_move_up.svg",
         "texture_displacement_move_down.svg", "texture_displacement_drag.svg",
         "texture_displacement_select_all.svg", "texture_displacement_erase_all.svg",
+        // Header help links: the video walkthrough and the wiki page.
+        "texture_displacement_video_guide.svg", "texture_displacement_wiki.svg",
     };
     std::vector<std::string> paths;
     paths.reserve(names.size());
@@ -5517,6 +5519,15 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
         ImGui::GetWindowDrawList()->AddRect(seg_min, ImVec2(ImGui::GetItemRectMax().x, seg_min.y + frame_h),
                                             ImGui::GetColorU32(col_frame), style.FrameRounding);
 
+        ImGui::SameLine(0.f, gap_s);
+        if (icon_button(807, "texture_displacement_video_guide.svg", icon_sm, _L("Video guide"),
+                        _L("Watch the texture displacement walkthrough on YouTube. Opens in your browser.")))
+            wxLaunchDefaultBrowser("https://www.youtube.com/watch?v=D7w3tG1kdvE");
+        ImGui::SameLine(0.f, gap_s);
+        if (icon_button(808, "texture_displacement_wiki.svg", icon_sm, _L("Documentation"),
+                        _L("Open the texture displacement page of the OrcaSlicer wiki. Opens in your browser.")))
+            wxLaunchDefaultBrowser("https://www.orcaslicer.com/wiki/print_prepare/prepare_texture_displacement.html");
+
         ImGui::SameLine(0.f, gap_s);
         if (icon_button(806, "canvas_drag.svg", icon_sm, m_undocked ? _L("Dock panel") : _L("Undock panel"),
                         _L("Detach this panel so it can be dragged anywhere over the 3D view, or dock it back beside "