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-ui/src/lib/forms/text-field.element.ts

@@ -46,6 +46,7 @@ export class TextFieldElement extends FormFieldBaseElement {
 		` : nothing}
 		<input
 			class="input"
+			part="input"
 			.type=${this.fieldType}
 			placeholder=${ifDefined(this.placeholder)}
 			.value=${this.value}