src/vs/workbench/contrib/customEditor/browser/customEditorInput.ts/CustomEditorInput/save
class CustomEditorInput:	public override async save(groupId: GroupIdentifier, options?: ISaveOptions): Promise<EditorInput | IUntypedEditorInput | undefined> {
		if (!this._modelRef) {
			return undefined;
		}

		const target = await this._modelRef.object.saveCustomEditor(options);
		if (!target) {
			return undefined; // save cancelled
		}

		// Different URIs == untyped input returned to allow resolver to possibly resolve to a different editor type
		if (!isEqual(target, this.resource)) {
			return { resource: target };
		}

		return this;
	}