[AccName] Label computation for elements with computed role of none

[giacomo-petri]

Ref: web-platform-tests/wpt#50002 (review)

I've removed from the PR all elements with an explicit or computed role of "none," as there's no reliable way to obtain a label from an ignored element.

I've also kept track of the created examples, so they're available if needed in the future.

<!-- This test case is specifically designed to check the accessible name, but a separate test case has been created in wai-aria/role/role_none_conflict_resolution.tentative.html to check the role -->
<h2>HTML input with role="none" and disabled with label associated</h2>
<h3>HTML input label/for</h3>
<label for="irpd">input label</label>
<input id="irpd" type="text" data-expectedlabel="" data-testname="html: label[for]+input[role=none][disabled] (role none applied due to disabled input)" class="ex-label" role="none" disabled>
<h3>HTML label encapsulation</h3>
<label>
      <span>input label</span>
      <input type="text" data-expectedlabel="" data-testname="html: label>input[role=none][disabled] (with label encapsulation, role none applied due to disabled input)" class="ex-label" role="none" disabled>
</label>

<h2>HTML img with role="none" and non empty alt</h2>
<img src="https://www.w3.org/assets/logos/w3c/w3c-no-bars.svg" role="none" alt="w3c logo" data-expectedlabel="" data-testname="html: img[role=none][alt]:not([alt='']) (role none takes precedence over empty alt)" class="ex-label">

<h2>HTML fieldset with role="none" wrapping legend</h2>
<fieldset role="none" data-expectedlabel="" data-testname="html: fieldset[role=none]>legend (role none set on fieldset affects fieldset acc name)" class="ex-label"><legend>legend</legend></fieldset>

<h2>HTML fieldset role="none" wrapping legend with role="none"</h2>
<fieldset role="none" data-expectedlabel="" data-testname="html: fieldset[role=none]>legend[role=none] (role none set on fieldset affects fieldset acc name)" class="ex-label"><legend role="none">legend</legend></fieldset>

<h2>HTML table with role="none" wrapping caption</h2>
<table role="none" data-expectedlabel="" data-testname="html: table[role=none]>caption (role none set on table affects fieldset acc name)" class="ex-label">
   <caption>caption</caption>
   <tr>
      <th>th1</th>
      <th>th2</th>
   </tr>
   <tr>
      <td>td1</td>
      <td>td2</td>
   </tr>
</table>

<h2>HTML table role="none" wrapping caption with role="none"</h2>
<table role="none" data-expectedlabel="" data-testname="html: table[role=none]>caption[role=none] (role none set on table affects fieldset acc name)" class="ex-label">
   <caption role="none">caption</caption>
   <tr>
      <th>th1</th>
      <th>th2</th>
   </tr>
   <tr>
      <td>td1</td>
      <td>td2</td>
   </tr>
</table>