Implement filled gizmos (#70)

Reviewed-on: #70
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/filled_gizmo.wgsl

@@ -0,0 +1,30 @@
+#import bevy_pbr::mesh_functions::{get_world_from_local, mesh_position_local_to_clip}
+
+@group(#{MATERIAL_BIND_GROUP}) @binding(0) var<uniform> material_color: vec4<f32>;
+
+struct Vertex {
+    @builtin(instance_index) instance_index: u32,
+    @location(0) position: vec3<f32>,
+    @location(1) color: vec4<f32>,
+};
+
+struct VertexOutput {
+    @builtin(position) clip_position: vec4<f32>,
+    @location(0) color: vec4<f32>,
+};
+
+@vertex
+fn vertex(vertex: Vertex) -> VertexOutput {
+    var output: VertexOutput;
+    output.clip_position = mesh_position_local_to_clip(
+        get_world_from_local(vertex.instance_index),
+        vec4<f32>(vertex.position, 1.0),
+    );
+    output.color = vertex.color;
+    return output;
+}
+
+@fragment
+fn fragment(input: VertexOutput) -> @location(0) vec4<f32> {
+    return material_color * input.color;
+}