Update IActionDescriptor.precondition desc (microsoft#176124)

* Update standaloneCodeEditor.ts

* Update comment and monaco.d.ts

---------

Co-authored-by: Alexandru Dima <[email protected]>

Author: PmcFizz

src/vs/editor/standalone/browser/standaloneCodeEditor.ts

@@ -55,7 +55,7 @@ export interface IActionDescriptor {
 	 */
 	label: string;
 	/**
-	 * Precondition rule.
+	 * Precondition rule. The value should be a [context key expression](https://code.visualstudio.com/docs/getstarted/keybindings#_when-clause-contexts).
 	 */
 	precondition?: string;
 	/**

src/vs/monaco.d.ts

@@ -1251,7 +1251,7 @@ declare namespace monaco.editor {
 		 */
 		label: string;
 		/**
-		 * Precondition rule.
+		 * Precondition rule. The value should be a [context key expression](https://code.visualstudio.com/docs/getstarted/keybindings#_when-clause-contexts).
 		 */
 		precondition?: string;
 		/**