Fix support interface semantics, gap handling, behavior; fix bottom interface generation for organic trees; fix non organic tree interfaces (#11812)

* Fix support interface semantics and gap handling

Fix zero-gap interface detection and gap initialization for supports and raft.
Ensures correct top/bottom contact semantics and avoids relying on default zero gaps.

* Additional fixes and robustness improvements

Fix incorrect coupling between top and bottom support interface spacing and density, ensuring bottom interfaces use their own parameters for smoothing and toolpath generation.
Restore correct bottom interface generation for organic (tree) supports when a non-zero bottom Z gap is used, and preserve contacts even when base polygons are empty.
Improve robustness of organic support slicing by fixing layer index drift and guarding against degenerate polygon boolean operations.

* Typo and semantics fix

differnt_support_interface_filament -> different_support_interface_filament

soluble -> zero_top_z_gap

* Fix non organic tree bottom support interface generation

Slim tree bottom interface layer numbers were capped by the object's layer number beneath it.
Fixed by refactoring the generation algorithm.

* Fix non organic tree interlaced support generation

Deterministic local interlaced support layers generation for non-organic tree support

* Enable support interface multimaterial for non organic tree

Enables mixed-material support interface behavior for non organic tree support type.

* Fix tree support interface layer counts and contact handling

- Correct non‑organic tree top interface layer budgeting so gaps don’t consume a layer (N stays N).
- Remove the extra roof interface pass that was duplicating the 2nd layer.
- Organic tree: use only the lowest contact footprint and avoid extra bottom‑contact extrusion so interface count matches the user setting.

* Bugfixes (a lot)

Many, many bugs fixed, majority edge-case but still not  playing by the rule.
Some of them:
- on multilevel base, on very small level variations the support was capped to the topmost level height
- non-organic tree had gaps for supports in a multilevel base situiation
- independent support layer height had issues with support interfaces (base support beneath bottom interface, top contact layer sometimes missing)
- organic tree had issues with small variation multi-level base
- organic tree support with zero top Z distance could overlap support-material and interface-material paths when separate materials were used
- many, many others (I lost track of them)

src/libslic3r/Support/TreeSupportCommon.hpp

@@ -306,7 +306,7 @@ public:
     
         layer_start_bp_radius = (bp_radius - branch_radius) / bp_radius_increase_per_layer;
     
-        if (TreeSupportSettings::soluble) {
+        if (TreeSupportSettings::zero_top_z_gap) {
             // safeOffsetInc can only work in steps of the size xy_min_distance in the worst case => xy_min_distance has to be a bit larger than 0 in this worst case and should be large enough for performance to not suffer extremely
             // When for all meshes the z bottom and top distance is more than one layer though the worst case is xy_min_distance + min_feature_size
             // This is not the best solution, but the only one to ensure areas can not lag though walls at high maximum_move_distance.
@@ -356,7 +356,7 @@ public:
 
     // some static variables dependent on other meshes that are not currently processed.
     // Has to be static because TreeSupportConfig will be used in TreeModelVolumes as this reduces redundancy.
-    inline static bool soluble = false;
+    inline static bool zero_top_z_gap = false;
     /*!
      * \brief Width of a single line of support.
      */
@@ -718,9 +718,15 @@ public:
     {
         assert(support_parameters.has_top_contacts);
         assert(dtt_roof <= support_parameters.num_top_interface_layers);
+        // ORCA: Reserve one top interface layer but only when top base-interface layers exist.
+        // This prevents all interface layers from being classified as base-interface layers
+        // and preserves correct top contact and interface behavior.
+        size_t interface_threshold = support_parameters.num_top_interface_layers_only();
+        if (interface_threshold > 0 && support_parameters.num_top_base_interface_layers > 0)
+            --interface_threshold;
         SupportGeneratorLayersPtr &layers =
             dtt_roof == 0 ? this->top_contacts :
-            dtt_roof <= support_parameters.num_top_interface_layers_only() ? this->top_interfaces : this->top_base_interfaces;
+            dtt_roof <= interface_threshold ? this->top_interfaces : this->top_base_interfaces;
         SupportGeneratorLayer*& l = layers[insert_layer_idx];
         if (l == nullptr)
             l = &layer_allocate_unguarded(layer_storage, dtt_roof == 0 ? SupporLayerType::TopContact : SupporLayerType::TopInterface,