Change scaling mode to FixedHorizontal (bevyengine#4055)

# Objective

- Fixes the issue with orthographic camera imported from glTF not displaying anything (mentioned in bevyengine#4005).

## Solution

- This was due to wrong scaling mode being used. This PR simply changes WindowSize scaling mode to FixedHorizontal.

## Important Note

Currently, othographic scale in Blender, three.js, and possibly other software does not translate to Bevy (via glTF) because their developers have [misinterpreted the spec](KhronosGroup/glTF#1663 (comment)). The camera parameters have been clarified in glTF 2.0, which was released on October of 2021. In Blender 3.0.1 this issue has **not** been fixed yet. If you are importing orthographic cameras from Blender, you have to divide the scale by 2.

crates/bevy_gltf/src/loader.rs

@@ -15,7 +15,8 @@ use bevy_pbr::{
 };
 use bevy_render::{
     camera::{
-        Camera, Camera2d, Camera3d, CameraProjection, OrthographicProjection, PerspectiveProjection,
+        Camera, Camera3d, CameraProjection, OrthographicProjection, PerspectiveProjection,
+        ScalingMode,
     },
     color::Color,
     mesh::{
@@ -721,22 +722,22 @@ fn load_node(
         match camera.projection() {
             gltf::camera::Projection::Orthographic(orthographic) => {
                 let xmag = orthographic.xmag();
-                let ymag = orthographic.ymag();
                 let orthographic_projection: OrthographicProjection = OrthographicProjection {
-                    left: -xmag,
-                    right: xmag,
-                    top: ymag,
-                    bottom: -ymag,
                     far: orthographic.zfar(),
                     near: orthographic.znear(),
+                    scaling_mode: ScalingMode::FixedHorizontal,
+                    scale: xmag / 2.0,
                     ..Default::default()
                 };
 
                 node.insert(Camera {
                     projection_matrix: orthographic_projection.get_projection_matrix(),
+                    near: orthographic_projection.near,
+                    far: orthographic_projection.far,
                     ..Default::default()
                 });
-                node.insert(orthographic_projection).insert(Camera2d);
+                node.insert(orthographic_projection);
+                node.insert(Camera3d);
             }
             gltf::camera::Projection::Perspective(perspective) => {
                 let mut perspective_projection: PerspectiveProjection = PerspectiveProjection {