Website: improve handlebars language support (#18554)

website/playground/panel/language.js

@@ -51,6 +51,8 @@ function getCodemirrorMode(parser) {
       return "YAML";
 
     case "glimmer":
+      return "Handlebars";
+
     case "html":
     case "mjml":
     case "lwc":
@@ -75,6 +77,12 @@ async function getLanguageExtension(mode) {
     return graphql();
   }
 
+  if (mode === "Handlebars") {
+    const { handlebarsLanguage } =
+      await import("@xiechao/codemirror-lang-handlebars");
+    return handlebarsLanguage;
+  }
+
   if (!languageExtensions) {
     const { languages } = await import("@codemirror/language-data");
     languageExtensions = new Map(