src/vs/workbench/api/common/extHostCustomEditors.ts/ExtHostCustomEditors/$onSaveAs
class ExtHostCustomEditors:	async $onSaveAs(resourceComponents: UriComponents, viewType: string, targetResource: UriComponents, cancellation: CancellationToken): Promise<void> {
		const entry = this.getCustomDocumentEntry(viewType, resourceComponents);
		const provider = this.getCustomEditorProvider(viewType);
		return provider.saveCustomDocumentAs(entry.document, URI.revive(targetResource), cancellation);
	}