feat(types): LangTag types languageName prop using LanguageName utility type

Author: metonym

src/LangTag.svelte

@@ -5,7 +5,7 @@
   /** @type {string} */
   export let highlighted;
 
-  /** @type {string} */
+  /** @type {import('./languages').LanguageName | (string & {})} */
   export let languageName = "plaintext";
 
   /** @type {boolean} */

src/LangTag.svelte.d.ts

@@ -1,6 +1,7 @@
 import type { SvelteComponentTyped } from "svelte";
 import type { HTMLAttributes } from "svelte/elements";
 import type { LangtagProps } from "./Highlight.svelte";
+import type { LanguageName } from "./languages";
 
 export type LangTagProps = HTMLAttributes<HTMLPreElement> &
   LangtagProps & {
@@ -18,7 +19,7 @@ export type LangTagProps = HTMLAttributes<HTMLPreElement> &
      * Provide the language name.
      * @default "plaintext"
      */
-    languageName?: string;
+    languageName?: LanguageName | (string & {});
   };
 
 export type LangTagEvents = {};