Targetable check, fix / complete implementation, polish

[vatro]

see (e.g.):

svelthree/src/components/SpotLight.svelte

Lines 257 to 261 in 5ef56b4

	/** Defaults to `true` which means that components / objects with targets (_`DirectionalLight`, `SpotLight`, `OrthographicCamera` and `PerspectiveCamera`_)
	* will add the built-in 'blank' target-Object3D to component's / object's parent on initialization. `target` can be either set to `false` ( TODO ) (_which will remove the target from parent only if it's
	* not the built-in 'blank' `Object3D`_) or some other object in the scene (_any `Object3D`, an `Empty` component or a `Mesh` component_) */
	export let target: Targetable | boolean = undefined
	$: if (target === undefined) target = true

target can be either set to false ( TODO )`

and

svelthree/src/utils/LightTarget.ts

Lines 35 to 39 in 5ef56b4

	} else if (typeof this.target === "boolean") {
	// light_comp_ref.target = true -> use the built-in 'Object3D' as target (add it to the scene)
	this.light["target"].userData.is_builtin_target = true
	this.scene.add(this.light["target"])
	}

[vatro]

This is a mess, will need a refactor:

• deprecate / drop target prop incl. related logic (use only lookAt prop)
• Lights with target: Fix / refactor target & lookAt logic incl. helper handling
• Fix / refactor PropUtils.setLookAtFromValue