Add line and linebox geom primitives.

PiperOrigin-RevId: 818570050
Change-Id: If02873dd878a23b442368ce69bc024e0310e9d02

src/experimental/filament/assets/unlit_line.mat

@@ -0,0 +1,29 @@
+// Copyright 2025 DeepMind Technologies Limited
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+material {
+    name : unlit_segmentation,
+    shadingModel : unlit,
+    culling: none,
+    parameters : [
+        { type : float4, name : BaseColorFactor }
+    ]
+}
+
+fragment {
+    void material(inout MaterialInputs material) {
+      prepareMaterial(material);
+      material.baseColor = materialParams.BaseColorFactor;
+    }
+}