fix: externalize prettier/plugins/estree to prevent bundling stale code

The vite config listed `prettier/plugins/estree.js` as external, but the
source imports `prettier/plugins/estree` (no .js extension). This mismatch
caused vite to bundle prettier's estree printer into the plugin instead of
keeping it external. When the user installs a newer version of prettier
(e.g. 3.6.2), the plugin still uses the old bundled estree code whose
`canAttachComment` function expects 2 arguments, while prettier 3.6+'s
core calls it with 1 argument. This causes a crash:

  TypeError: undefined is not iterable (cannot read property Symbol(Symbol.iterator))

when formatting any .gts file that contains both a comment and a <template> tag.

The fix removes the .js extension from the external config so it matches
the actual import paths. Also adds a regression test case.

Closes #424

Author: lifeart

tests/cases/gts/comment-with-template.gts

@@ -0,0 +1,4 @@
+// A comment before template
+<template>
+  <div>hello</div>
+</template>

tests/unit-tests/__snapshots__/format.test.ts.snap

@@ -295,6 +295,14 @@ const three = <template>{{if true "true"}}</template>;
 "
 `;
 
+exports[`format > config > default > it formats ../cases/gts/comment-with-template.gts 1`] = `
+"// A comment before template
+<template>
+  <div>hello</div>
+</template>
+"
+`;
+
 exports[`format > config > default > it formats ../cases/gts/complex.gts 1`] = `
 "import { on } from "@ember/modifier";
 import { service } from "@ember/service";

tests/unit-tests/config/__snapshots__/semi-false.test.ts.snap

@@ -295,6 +295,14 @@ const three = <template>{{if true "true"}}</template>
 "
 `;
 
+exports[`config > semi: false > it formats ../cases/gts/comment-with-template.gts 1`] = `
+"// A comment before template
+<template>
+  <div>hello</div>
+</template>
+"
+`;
+
 exports[`config > semi: false > it formats ../cases/gts/complex.gts 1`] = `
 "import { on } from "@ember/modifier"
 import { service } from "@ember/service"

tests/unit-tests/config/__snapshots__/template-export-default.test.ts.snap

@@ -295,6 +295,14 @@ const three = <template>{{if true "true"}}</template>;
 "
 `;
 
+exports[`config > templateExportDefault: true > it formats ../cases/gts/comment-with-template.gts 1`] = `
+"// A comment before template
+<template>
+  <div>hello</div>
+</template>
+"
+`;
+
 exports[`config > templateExportDefault: true > it formats ../cases/gts/complex.gts 1`] = `
 "import { on } from "@ember/modifier";
 import { service } from "@ember/service";

vite.config.mjs

@@ -6,8 +6,8 @@ export default defineConfig({
       external: [
         'content-tag',
         'prettier',
-        'prettier/plugins/estree.js',
-        'prettier/plugins/babel.js',
+        'prettier/plugins/estree',
+        'prettier/plugins/babel',
       ],
     },
     lib: {