Inspector editing (#96)

This PR adds Material component inspection to the frontend Entity
Inspector, and adds functional editing capabilities for the Transform
and Material inspectors.

### Changes
* Added a `ScalarFieldElement` for numeric form fields, with a hybrid
slider/text-input UX inspired by Blender, Unreal Engine, etc.
* Added `MaterialInspectorElement` for inspecting the Bevy
`StandardMaterial` component
* Wired up the `TransformInspectorElement` and
`MaterialInspectorElement` to apply changes made in the UI to the Bevy
scene
* Refactored the `studio/ui/inspector` module to output `Result::Err`s
to the dev console
* Refactored the `studio/interaction/selection` module to use only the
`Selection` resource, removing the redundant `Selected` component which
added some unnecessary complexity. This fixes #39
* Fixed primitive shapes not receiving a selection outline when selected

### To-Do

These tasks will be addressed in a forthcoming PR:

* The **Transform** > **Rotation** section in the inspector is still not
displaying sensible values. Currently it's just displaying the raw
quaternion `xyz` vector rather than displaying the orientation in
human-readable terms (e.g., as Euler angles).
* We're currently ignoring the Primitive Shape component, which would
allow the user to configure some additional geometric properties of the
shape or replace it with a different one.

---------

Co-authored-by: rewin <rewin1996@gmail.com>

studio/src/scene.rs

@@ -17,7 +17,10 @@ use bevy::{
 use serde_repr::{Deserialize_repr, Serialize_repr};
 use space_editor::{
     prelude::{EditorEvent, EditorPrefabPath, PrefabMarker},
-    space_prefab::component::{GltfPrefab, SceneAutoChild},
+    space_prefab::{
+        component::{GltfPrefab, SceneAutoChild},
+        editor_registry::EditorRegistryExt,
+    },
 };
 #[cfg(feature = "wasm")]
 use wasm_bindgen::prelude::wasm_bindgen;
@@ -109,6 +112,8 @@ impl Plugin for ScenePlugin {
                 wasm::notify_loading_queue_changes.map(bevy::utils::error),
             ),
         );
+
+        app.editor_registry::<SceneElement>();
     }
 }
 
@@ -253,9 +258,11 @@ pub struct ImportSceneEvent(pub String);
     wasm_bindgen,
     derive(Serialize_repr, Deserialize_repr)
 )]
-#[derive(Component, Clone, Copy, Debug, PartialEq, Eq)]
+#[derive(Component, Clone, Copy, Debug, PartialEq, Eq, Reflect, Default)]
+#[reflect(Component, Default)]
 #[allow(dead_code)] // Some variants only used in `wasm`, some planned for later use
 pub enum SceneElement {
+    #[default]
     Generic,
     Mesh,
     Skeleton,