Enable semantic features in interactive playground

Fixes #109190

extensions/typescript-language-features/src/utils/documentSelector.ts

@@ -9,10 +9,10 @@ export interface DocumentSelector {
 	/**
 	 * Selector for files which only require a basic syntax server.
 	 */
-	readonly syntax: vscode.DocumentFilter[];
+	readonly syntax: readonly vscode.DocumentFilter[];
 
 	/**
 	 * Selector for files which require semantic server support.
 	 */
-	readonly semantic: vscode.DocumentFilter[];
+	readonly semantic: readonly vscode.DocumentFilter[];
 }

extensions/typescript-language-features/src/utils/fileSchemes.ts

@@ -13,6 +13,7 @@ export const walkThroughSnippet = 'walkThroughSnippet';
 export const semanticSupportedSchemes = [
 	file,
 	untitled,
+	walkThroughSnippet,
 ];
 
 /**