Combine brims option (Prusa style brims) (#12343)

* Union ex brims

Revert "Union ex brims"

This reverts commit bbc9a39faf318dc2df093eb2bdcebf19a4162fe9.

Update Brim.cpp

* dont repeat paths

* Update Brim.cpp

* multimaterial brim independiente

* Normal brim if is by object

* fix print order

* cleaning 1

* cleaning 2

* Normal brim if multimaterial on first layer

* fix artifact

* combine_brim optional

refactoring

* refactoring gcode.cpp

* refactoring brim.cpp

Update Brim.cpp

* Remove multimaterial first-layer check for brims

Stop detecting extruders used on the first layer and remove the is_multimaterial_first_layer guard. Simplify can_combine_brims to only consider combine_brims and whether printing is ByObject, allowing brims to be combined across extruders unless printing by object or combine_brims is disabled. Cleans up unused code and simplifies brim-generation conditions.

* Remove material specification from unified brim comment

* Update PrintConfig.cpp

src/libslic3r/PrintConfig.hpp

@@ -1550,6 +1550,7 @@ PRINT_CONFIG_CLASS_DERIVED_DEFINE(
     ((ConfigOptionString,             thumbnails))
     // BBS: move from PrintObjectConfig
     ((ConfigOptionBool, independent_support_layer_height))
+    ((ConfigOptionBool,               combine_brims))
     // SoftFever
     ((ConfigOptionPercents,            filament_shrink))
     ((ConfigOptionPercents,            filament_shrinkage_compensation_z))