New modifier for grease pencil outlines.

In principle generating separate inside/outside perimeters is better,
but the renderer does not support holes in cyclic curves atm, so the
GPv2 method with end caps is preferable.

@@ -0,0 +121,4 @@
+namespace array_utils {
+
+template<typename T>
+inline void rotate_group_to_group(const OffsetIndices<int> src_offsets,

@@ -0,0 +674,4 @@
+  using bke::greasepencil::Layer;
+  using modifier::greasepencil::LayerDrawingInfo;
+
+  auto *omd = reinterpret_cast<GreasePencilOutlineModifierData *>(md);

@@ -0,0 +707,4 @@
+
+  PointerRNA ob_ptr;
+  PointerRNA *ptr = modifier_panel_get_property_pointers(panel, &ob_ptr);
+  // auto *omd = static_cast<GreasePencilOutlineModifierData *>(ptr->data);

@@ -0,0 +108,4 @@
+      ctx->node, ctx->object, DEG_OB_COMP_TRANSFORM, "Grease Pencil Outline Modifier");
+}
+
+static bke::CurvesGeometry reorder_cyclic_curve_points(const bke::CurvesGeometry &src_curves,

@@ -0,0 +128,4 @@
+      return;
+    }
+    const int shift_raw = curve_offsets[curve_i];
+    const int shift = shift_raw >= 0 ? shift_raw % points.size() :

@@ -0,0 +153,4 @@
+static int find_closest_point(const Span<float3> positions, const float3 &target)
+{
+  if (positions.is_empty()) {
+    return -1;

@@ -0,0 +152,4 @@
+   * source indices are not ordered. */
+  bke::CurvesGeometry dst_curves(src_curves);
+  bke::MutableAttributeAccessor dst_attributes = dst_curves.attributes_for_write();
+  bke::gather_attributes(src_attributes, bke::AttrDomain::Point, {}, {}, indices, dst_attributes);