fix: ignore comment + whitespace nodes in template-no-yield-only

The rule flagged yield-only templates by asserting
`templateNodes.length === 1 && isYieldOnly(templateNodes[0])`. That
works only while the parser strips template comments out of the body,
which ember-estree 0.4.2 happened to do. Upstream ember-estree 0.4.3
(#31) began keeping MustacheCommentStatement nodes in the body, so a
template like

    <template>{{! some comment }}{{yield}}</template>

now yields a body of length 2 and silently stops being flagged — which
is also why PR #2735 (upgrade to ember-eslint-parser 0.11) fails this
rule's CI.

Ignoring comment and whitespace-only text nodes before the length check
aligns with:

- upstream ember-template-lint's `no-yield-only.js` (unchanged there
  since comments-in-body is the native Glimmer AST shape anyway)
- the sibling rule `template-no-bare-yield.js`, which already uses the
  same `isEmptyNode` filter

The fix is a no-op on the currently-pinned ember-eslint-parser@0.10 and
fixes the rule under any parser version that preserves comment nodes in
the template body. The rule also now correctly catches yield-only
templates that contain HTML comments (`<!-- x -->{{yield}}`), which it
was silently missing before.

Author: johanrd

lib/rules/template-no-yield-only.js

@@ -1,3 +1,11 @@
+function isEmptyNode(node) {
+  return (
+    node.type === 'GlimmerMustacheCommentStatement' ||
+    node.type === 'GlimmerCommentStatement' ||
+    (node.type === 'GlimmerTextNode' && !node.chars.trim())
+  );
+}
+
 function isYieldOnly(node) {
   return (
     node.type === 'GlimmerMustacheStatement' &&
@@ -44,7 +52,8 @@ module.exports = {
             ? node.body[0].children
             : node.body;
 
-        if (templateNodes.length === 1 && isYieldOnly(templateNodes[0])) {
+        const nonEmptyNodes = templateNodes.filter((n) => !isEmptyNode(n));
+        if (nonEmptyNodes.length === 1 && isYieldOnly(nonEmptyNodes[0])) {
           isOnlyYield = true;
         }
       },

tests/lib/rules/template-no-yield-only.js

@@ -30,6 +30,16 @@ const invalidHbs = [
     output: null,
     errors: [{ messageId: 'noYieldOnly' }],
   },
+  {
+    code: '{{!-- long-form comment --}}{{yield}}',
+    output: null,
+    errors: [{ messageId: 'noYieldOnly' }],
+  },
+  {
+    code: '<!-- html comment -->{{yield}}',
+    output: null,
+    errors: [{ messageId: 'noYieldOnly' }],
+  },
 ];
 
 function wrapTemplate(entry) {