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/SupportMaterial.cpp

@@ -1739,7 +1739,7 @@ static inline std::pair<SupportGeneratorLayer*, SupportGeneratorLayer*> new_cont
         print_z  = slicing_params.raft_contact_top_z;
         bottom_z = slicing_params.raft_interface_top_z;
         height   = slicing_params.contact_raft_layer_height;
-    } else if (slicing_params.soluble_interface) {
+    } else if (slicing_params.zero_gap_interface_top) {
         // Align the contact surface height with a layer immediately below the supported layer.
         // Interface layer will be synchronized with the object.
         print_z  = layer.bottom_z();
@@ -1862,7 +1862,7 @@ static inline void fill_contact_layer(
 #endif // SLIC3R_DEBUG
         ));
     // 2) infill polygons, expand them by half the extrusion width + a tiny bit of extra.
-    bool reduce_interfaces = object_config.support_style.value != smsSnug && layer_id > 0 && !slicing_params.soluble_interface;
+    bool reduce_interfaces = object_config.support_style.value != smsSnug && layer_id > 0 && !slicing_params.zero_gap_interface_top;
     if (reduce_interfaces) {
         // Reduce the amount of dense interfaces: Do not generate dense interfaces below overhangs with 60% overhang of the extrusions.
         Polygons dense_interface_polygons = diff(overhang_polygons, lower_layer_polygons_for_dense_interface());
@@ -2421,12 +2421,12 @@ static inline SupportGeneratorLayer* detect_bottom_contacts(
     Layer* upper_layer = layer.upper_layer;
     if (object.print()->config().independent_support_layer_height) {
         // If the layer is extruded with no bridging flow, support just the normal extrusions.
-        layer_new.height = slicing_params.soluble_interface ?
+        layer_new.height = slicing_params.zero_gap_interface_bottom ?
             // Align the interface layer with the object's layer height.
             upper_layer->height :
             // Place a bridge flow interface layer or the normal flow interface layer over the top surface.
             support_params.support_material_bottom_interface_flow.height();
-        layer_new.print_z = slicing_params.soluble_interface ? upper_layer->print_z :
+        layer_new.print_z = slicing_params.zero_gap_interface_bottom ? upper_layer->print_z :
             layer.print_z + layer_new.height + slicing_params.gap_object_support;
     }
     else {
@@ -2436,11 +2436,11 @@ static inline SupportGeneratorLayer* detect_bottom_contacts(
     }
     layer_new.bottom_z = layer.print_z;
     layer_new.idx_object_layer_below = layer_id;
-    layer_new.bridging = !slicing_params.soluble_interface && object.config().thick_bridges;
+    layer_new.bridging = !slicing_params.zero_gap_interface_bottom && object.config().thick_bridges;
     //FIXME how much to inflate the bottom surface, as it is being extruded with a bridging flow? The following line uses a normal flow.
     layer_new.polygons = expand(touching, float(support_params.support_material_flow.scaled_width()), SUPPORT_SURFACES_OFFSET_PARAMETERS);
 
-    if (! slicing_params.soluble_interface) {
+    if (!slicing_params.zero_gap_interface_bottom) {
         // Walk the top surfaces, snap the top of the new bottom surface to the closest top of the top surface,
         // so there will be no support surfaces generated with thickness lower than m_support_layer_height_min.
         for (size_t top_idx = size_t(std::max<int>(0, contact_idx));
@@ -2909,7 +2909,7 @@ SupportGeneratorLayersPtr PrintObjectSupportMaterial::raft_and_intermediate_supp
                 // Continue printing the other layers up to extr2z.
                 step = dist / coordf_t(n_layers_extra);
             }
-            if (! m_slicing_params.soluble_interface && extr2->layer_type == SupporLayerType::TopContact) {
+            if (!m_slicing_params.zero_gap_interface_top && extr2->layer_type == SupporLayerType::TopContact) {
                 // This is a top interface layer, which does not have a height assigned yet. Do it now.
                 assert(extr2->height == 0.);
                 assert(extr1z > m_slicing_params.first_print_layer_height - EPSILON);
@@ -3170,7 +3170,7 @@ void PrintObjectSupportMaterial::trim_support_layers_by_object(
                         polygons_append(polygons_trimming, offset({ expoly }, trimming_offset, SUPPORT_SURFACES_OFFSET_PARAMETERS));
                     }
                 }
-                if (! m_slicing_params.soluble_interface && m_object_config->thick_bridges) {
+                if (!m_slicing_params.zero_gap_interface_top && m_object_config->thick_bridges) {
                     // Collect all bottom surfaces, which will be extruded with a bridging flow.
                     for (; i < object.layers().size(); ++ i) {
                         const Layer &object_layer = *object.layers()[i];