Unignore Camera.target field for reflection (#14367)

# Objective

- The `RenderTarget` type wasn't being registered, and the `target`
field of `Camera` was marked as ignored, so it wasn't inspectable by
editors.

## Solution

- Remove `#[reflect(ignore)]` from the field
- I've also reordered the `Default` impl of `RenderTarget` because it
looked like it belonged to a different type

crates/bevy_render/src/camera/camera.rs

@@ -211,7 +211,6 @@ pub struct Camera {
     #[reflect(ignore)]
     pub computed: ComputedCameraValues,
     /// The "target" that this camera will render to.
-    #[reflect(ignore)]
     pub target: RenderTarget,
     /// If this is set to `true`, the camera will use an intermediate "high dynamic range" render texture.
     /// This allows rendering with a wider range of lighting values.
@@ -541,6 +540,12 @@ pub enum RenderTarget {
     TextureView(ManualTextureViewHandle),
 }
 
+impl Default for RenderTarget {
+    fn default() -> Self {
+        Self::Window(Default::default())
+    }
+}
+
 impl From<Handle<Image>> for RenderTarget {
     fn from(handle: Handle<Image>) -> Self {
         Self::Image(handle)
@@ -561,12 +566,6 @@ pub enum NormalizedRenderTarget {
     TextureView(ManualTextureViewHandle),
 }
 
-impl Default for RenderTarget {
-    fn default() -> Self {
-        Self::Window(Default::default())
-    }
-}
-
 impl RenderTarget {
     /// Normalize the render target down to a more concrete value, mostly used for equality comparisons.
     pub fn normalize(&self, primary_window: Option<Entity>) -> Option<NormalizedRenderTarget> {