fix(template-anchor-has-content): unwrap mustache literals via shared helper (Copilot review)

Extract a new `getStaticAttrValue` util that resolves literal-valued
mustaches (`{{"foo"}}`, `{{true}}`, `{{-1}}`) and single-part concat
statements (`"{{true}}"`) to their static string value. `isAriaHiddenTrue`
now delegates to the helper, so quoted-mustache forms of aria-hidden
(e.g. `<a aria-hidden="{{true}}">link</a>`) are recognised the same as
their text-node counterparts when walking descendants for accessible
content.

Byte-identical carrier of lib/utils/static-attr-value.js across all PRs
that land it.

Author: johanrd

lib/rules/template-anchor-has-content.js

@@ -1,32 +1,28 @@
 const { isNativeElement } = require('../utils/is-native-element');
+const { getStaticAttrValue } = require('../utils/static-attr-value');
 
 function isDynamicValue(value) {
   return value?.type === 'GlimmerMustacheStatement' || value?.type === 'GlimmerConcatStatement';
 }
 
 // Returns true if the `aria-hidden` attribute is explicitly set to "true"
-// (case-insensitive) or mustache-literal `{{true}}`. Per WAI-ARIA 1.2 §6.6
-// + aria-hidden value table, valueless / empty-string `aria-hidden` resolves
-// to the default `undefined` — NOT `true` — so those forms do NOT hide the
+// (case-insensitive) or mustache-literal `{{true}}` / `{{"true"}}` / the
+// quoted-mustache concat equivalents. Per WAI-ARIA 1.2 §6.6 + aria-hidden
+// value table, valueless / empty-string `aria-hidden` resolves to the
+// default `undefined` — NOT `true` — so those forms do NOT hide the
 // element per spec. This aligns with the spec-first decisions in #2717 /
-// #19 / #33, and diverges from jsx-a11y's JSX-coercion convention.
+// #19 / #33, and diverges from jsx-a11y's JSX-coercion convention. All
+// shape-unwrapping is delegated to the shared `getStaticAttrValue` helper.
 function isAriaHiddenTrue(attr) {
-  if (!attr?.value) {
+  if (!attr) {
     return false;
   }
-  if (attr.value.type === 'GlimmerTextNode') {
-    return attr.value.chars.trim().toLowerCase() === 'true';
-  }
-  if (attr.value.type === 'GlimmerMustacheStatement') {
-    const path = attr.value.path;
-    if (path?.type === 'GlimmerBooleanLiteral') {
-      return path.value === true;
-    }
-    if (path?.type === 'GlimmerStringLiteral') {
-      return path.value.trim().toLowerCase() === 'true';
-    }
+  const resolved = getStaticAttrValue(attr.value);
+  if (resolved === undefined) {
+    // Dynamic — can't prove truthy.
+    return false;
   }
-  return false;
+  return resolved.trim().toLowerCase() === 'true';
 }
 
 // True if the anchor itself declares an accessible name via a statically