Improve presentation/none check to be case-insensitive

Per WAI-ARIA 1.2 spec: "Case-sensitivity of the comparison inherits
from the case-sensitivity of the host language" — and HTML is
case-insensitive. This improves on the original ember-template-lint
which inconsistently uses case-insensitive matching for VALID_ROLES
but case-sensitive for the presentation/none check.

Ref: https://www.w3.org/TR/wai-aria-1.2/#document-handling_author-errors_roles

Author: johanrd

lib/rules/template-no-invalid-role.js

@@ -242,7 +242,9 @@ module.exports = {
           return;
         }
 
-        // Check for presentation/none role on semantic elements
+        // Check for presentation/none role on semantic elements (case-insensitive per WAI-ARIA 1.2:
+        // "Case-sensitivity of the comparison inherits from the case-sensitivity of the host language"
+        // and HTML is case-insensitive — https://www.w3.org/TR/wai-aria-1.2/#document-handling_author-errors_roles)
         if (
           (roleLower === 'presentation' || roleLower === 'none') &&
           SEMANTIC_ELEMENTS.has(node.tag)