deprecate es5ClassCompat and explain why

Author: jrieken

src/vs/workbench/api/common/extHostTypes.ts

@@ -19,6 +19,12 @@ import { IRelativePatternDto } from 'vs/workbench/api/common/extHost.protocol';
 import { CellEditType, ICellPartialMetadataEdit, IDocumentMetadataEdit } from 'vs/workbench/contrib/notebook/common/notebookCommon';
 import type * as vscode from 'vscode';
 
+/**
+ * @deprecated
+ *
+ * This utility ensures that old JS code that uses functions for classes still works. Existing usages cannot be removed
+ * but new ones must not be added
+ * */
 function es5ClassCompat(target: Function): any {
 	///@ts-expect-error
 	function _() { return Reflect.construct(target, arguments, this.constructor); }