Merge upstream/main into belt-printer

Brings belt-printer up to main 4b4a261787. Resolutions:

- G-code header (#15897, #15915): main moved the header, config and
  thumbnail block later in _do_export; write_belt_header() moves with it,
  still after the thumbnails and outside the BTT_TFT gate.
- _extrude: first-layer acceleration keeps the per-path first-layer plane
  test with main's cached nozzle index (#16028); main's set_speed out-param
  form (#16108) everywhere else.
- GCodeWriter (#16108): the arc-to-polyline fallback for machine mappings
  that cannot express G2/G3 now runs in the out-param extrude_arc_to_xy,
  which is the overload GCode calls, and appends to the caller's string.
- GCodeProcessorResult: the belt fields join main's forwarding assign.
- Clipper2 (#15969): belt arrange helpers take Slic3r::Point; the tree
  support join types lose their ClipperLib qualifier.
- CLI arrange (#15837): belt printers still reserve no wipe tower.
- Wipe tower options (#15841): the two new sparse-layer toggles are hidden
  for belt printers like the rest of the tower options.
- Keyboard shortcuts (#15706): main's registry replaces the old key switch;
  the belt view toggle is re-registered in the next commit.
- Print::process: the belt purge-plan undo runs before main's SliceStarted
  event.
- scripts/filament_id_snapshot.json: deleted on main (a77209af8f).
- Includes and appended tests: union of both sides.

src/slic3r/GUI/3DBed.cpp

@@ -15,11 +15,27 @@
 #include "Plater.hpp"
 #include "Camera.hpp"
 
+#include <boost/version.hpp>
+#include <cstddef>
+#include <array>
 #include <glad/gl.h>
 
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/filesystem/operations.hpp>
 #include <boost/log/trivial.hpp>
+#include "slic3r/GUI/GLModel.hpp"
+#include <vector>
+#include "libslic3r/Point.hpp"
+#include <utility>
+#include "libslic3r/Color.hpp"
+#include "slic3r/GUI/ImGuiWrapper.hpp"
+#include "slic3r/GUI/GLShader.hpp"
+#include "slic3r/GUI/3DScene.hpp"
+#include "libslic3r/Geometry.hpp"
+#include <math.h>
+#include <tuple>
+#include "libslic3r/Preset.hpp"
+#include "libslic3r/Config.hpp"
 
 #if BOOST_VERSION >= 107800
 #include <boost/timer/timer.hpp>
@@ -627,6 +643,12 @@ void Bed3D::update_model_offset()
     shift(2) = -0.03;
     Vec3d* model_offset_ptr = const_cast<Vec3d*>(&m_model_offset);
     *model_offset_ptr = shift;
+    //BBS: TODO: hack for current stl for BBL printer
+    if (std::string::npos != m_model_filename.find("bbl-3dp-"))
+    {
+        (*model_offset_ptr)(0) -= m_bed_shape[2].x() / 2.0f;
+        (*model_offset_ptr)(1) -= m_bed_shape[2].y() / 2.0f;
+    }
     (*model_offset_ptr)(2) = -0.41 + GROUND_Z;
 
     // update extended bounding box