Validator rollup (#40223)

* cl/610820873 Fix validation for unexpected attribute name starting with =

* cl/614818595 Fix validation for duplicate attribute names

* cl/713373388 Two-way sync for PR #40094. No-op, or fixes merge conflicts, if any.

* Update some files that failed validator test

* Update some files that failed validator test

Author: banaag

validator/testdata/feature_tests/duplicate_attribute.out.cpponly

@@ -46,4 +46,4 @@ feature_tests/duplicate_attribute.html:27:3 The tag 'script' contains the attrib
 feature_tests/duplicate_attribute.html:27:3 The attribute 'type' in tag 'script type=application/ld+json' is set to the invalid value 'text/javascript'.
 |
 |  </body>
-|  </html>
+|  </html>

validator/testdata/feature_tests/leaks.html

@@ -35,6 +35,11 @@
 -->
 <meta http-equiv="refresh" content="10; url=http://leaking.via/meta-refresh">
 
+<!--
+%Redirects (empty attribute)
+-->
+<meta = http-equiv="refresh" content="10; url=http://leaking.via/meta-refresh">
+
 <!--
 %CSP
 -->

validator/testdata/feature_tests/leaks.out

@@ -53,6 +53,13 @@ feature_tests/leaks.html:30:4 CSS syntax error in tag 'style amp-custom' - saw i
 feature_tests/leaks.html:36:0 The attribute 'http-equiv' may not appear in tag 'meta'.
 |
 |  <!--
+|  %Redirects (empty attribute)
+|  -->
+|  <meta = http-equiv="refresh" content="10; url=http://leaking.via/meta-refresh">
+>> ^~~~~~~~~
+feature_tests/leaks.html:41:0 The attribute 'http-equiv' may not appear in tag 'meta'.
+|
+|  <!--
 |  %CSP
 |  -->
 |  <meta http-equiv="Content-Security-Policy" content="script-src 'self'; report-uri http://leaking.via/meta-csp-report-uri">
@@ -364,4 +371,4 @@ feature_tests/leaks.html:203:0 The tag 'vmlframe' is disallowed.
 |  </vmlframe>
 |
 |  </body>
-|  </html>
+|  </html>