Always register the Smooth Trimesh Collision project setting

This ensures the project setting never disappears from the editor,
even if the current physics engine is GodotPhysics.

This also adds documentation for the Smooth Trimesh Collision
project setting.

core/config/project_settings.cpp

@@ -1240,6 +1240,9 @@ ProjectSettings::ProjectSettings() {
 	custom_prop_info["rendering/driver/threads/thread_model"] = PropertyInfo(Variant::INT, "rendering/driver/threads/thread_model", PROPERTY_HINT_ENUM, "Single-Unsafe,Single-Safe,Multi-Threaded");
 	GLOBAL_DEF("physics/2d/run_on_separate_thread", false);
 	GLOBAL_DEF("physics/3d/run_on_separate_thread", false);
+	// Required to make the project setting appear even if the physics engine is GodotPhysics,
+	// while also making it appear in the ProjectSettings class documentation.
+	GLOBAL_DEF("physics/3d/smooth_trimesh_collision", false);
 
 	GLOBAL_DEF("debug/settings/profiler/max_functions", 16384);
 	custom_prop_info["debug/settings/profiler/max_functions"] = PropertyInfo(Variant::INT, "debug/settings/profiler/max_functions", PROPERTY_HINT_RANGE, "128,65535,1");

doc/classes/ProjectSettings.xml

@@ -1504,6 +1504,10 @@
 		<member name="physics/3d/sleep_threshold_linear" type="float" setter="" getter="" default="0.1">
 			Threshold linear velocity under which a 3D physics body will be considered inactive. See [constant PhysicsServer3D.SPACE_PARAM_BODY_LINEAR_VELOCITY_SLEEP_THRESHOLD].
 		</member>
+		<member name="physics/3d/smooth_trimesh_collision" type="bool" setter="" getter="" default="false">
+			If [code]true[/code], smooths out collision with trimesh shapes ([ConcavePolygonShape3D]) by telling the Bullet physics engine to generate internal edge information for every trimesh shape created.
+			[b]Note:[/b] Only effective if [member physics/3d/physics_engine] is set to [code]Bullet[/code], [i]not[/i] [code]DEFAULT[/code] or [code]GodotPhysics[/code].
+		</member>
 		<member name="physics/3d/solver/contact_max_allowed_penetration" type="float" setter="" getter="" default="0.01">
 			Maximum distance a shape can penetrate another shape before it is considered a collision. See [constant PhysicsServer3D.SPACE_PARAM_CONTACT_MAX_ALLOWED_PENETRATION].
 		</member>

modules/bullet/shape_bullet.cpp

@@ -422,7 +422,7 @@ void ConcavePolygonShapeBullet::setup(Vector<Vector3> p_faces) {
 
 		meshShape = bulletnew(btBvhTriangleMeshShape(shapeInterface, useQuantizedAabbCompression));
 
-		if (GLOBAL_DEF("physics/3d/smooth_trimesh_collision", false)) {
+		if (GLOBAL_GET("physics/3d/smooth_trimesh_collision")) {
 			btTriangleInfoMap *triangleInfoMap = new btTriangleInfoMap();
 			btGenerateInternalEdgeInfo(meshShape, triangleInfoMap);
 		}