Editor: Enhance SetValueCommand to support nested attributeName

[ycw]

fix: #28601

This PR enhances SetValueCommand to support nested attributeName, s.t. editor will dispatch objectChanged on object(which is the selected object), not object.shadow(which can never be a selected object) ...

// do this
new SetValueCommand(editor, object, 'shadow.intensity',...) // dispatch objectChanged on `object`

// instead of this
new SetValueCommand(editor, object.shadow, 'intensity',...) // disptach objectChanged on `object.shadow`

... which in turn UI will get refresh:

three.js/editor/js/Sidebar.Object.js

Lines 733 to 739 in 8eccd73

	signals.objectChanged.add( function ( object ) {
	if ( object !== editor.selected ) return;
	updateUI( object );
	} );

Preview: https://raw.githack.com/ycw/three.js/editor-setvaluecommand-attributename-supports-nested-props/editor/index.html
Test file: File>Open project.json
Test:

1. Select DirectionalLight in SCENE outliner
2. Change shadow intensity from 1.0 to 0.2 in OBJECT tab
3. Edit>Undo
4. You should see shadow intensity field is 1.0

SetValueCommand.supports.nested.properties.mp4

[Mugen87]

This creates an unnecessary complexity in SetValueCommand. I've filed a different PR that solves the issue more consistent so light shadows are treated like geometries and materials, see #28608.

[ycw]

good

[Mugen87]

Closing in favor of #28608.