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/camera_controller.rs

@@ -6,8 +6,8 @@ use bevy::{
 };
 
 use crate::{
-    input::{Action, CameraMotion, InputAction, Lifecycle, Selection},
-    interaction::Selected,
+    input::{self, Action, CameraMotion, InputAction, Lifecycle},
+    interaction::Selection,
     math::{
         Easing, InterpPosition, InterpVelocity, Interpolation, InterpolationSystem, NearlyEq,
         NearlyZero, Velocity,
@@ -155,20 +155,25 @@ fn process_physical_inputs(
 
 fn process_focus_inputs(
     mut cmd: Commands,
+    r_selection: Option<Res<Selection>>,
     mut input: EventReader<InputAction>,
     mut q_camera: Query<(Entity, &CameraController, &mut Velocity)>,
     q_interp_vel: Query<&InterpVelocity>,
     mut q_interp_pos: Query<&mut InterpPosition>,
-    q_selected_xform: Query<&GlobalTransform, With<Selected>>,
+    q_global_xforms: Query<&GlobalTransform>,
 ) {
+    let Some(selection) = r_selection else {
+        return;
+    };
+
     if input.read().any(|action| {
         matches!(
             action,
-            InputAction(Lifecycle::Stop, Action::Selection(Selection::Focus))
+            InputAction(Lifecycle::Stop, Action::Selection(input::Selection::Focus))
         )
     }) {
-        let Ok(target) = q_selected_xform
-            .get_single()
+        let Ok(target) = q_global_xforms
+            .get(**selection)
             .map(|xform| xform.translation())
         else {
             return;