Mark DocumentSelector as readonly (#109212)

This change:

- Make  `DocumentSelector` use a readonly array
- Updates all properties of `DocumentFilter` to be readonly

`DocumentSelector` is used as a parameter in our provider APIs and does not need to be mutable. This change lets extensions pass in readonly values for the selector

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[];
 }