Be more forgiving in specifying anchors

[garvinhicking]

Feature request

An anchors requires this markup:

.. _feature-99911-1675976882:

========================================
Feature: #99911 - New TCA type "country"
========================================

to produce this HTML (in render-guides as an example, custom HTML applied):

<section class="section" id="feature-99911-new-tca-type-country" data-rst-anchor="feature-99911-1675976882">
<a id="feature-99911-1675976882"></a>
            <h1>Feature: #99911 - New TCA type &quot;country&quot;<a class="headerlink" href="#feature-99911-new-tca-type-country"
            data-bs-toggle="modal" data-bs-target="#linkReferenceModal"
            title="Reference this headline"><i class="fa-solid fa-paragraph"></i></a></h1>
</section>

However, if someone forgets the whitespace and uses:

..  _typo3-cms-system-notes:
======================
TYPO3 CMS System Notes
======================

it will create:

<section class="section" id="typo3-cms-system-notes">
<h1>..  _typo3-cms-system-notes:<a class="headerlink" href="#typo3-cms-system-notes" data-bs-toggle="modal" data-bs-target="#linkReferenceModal"  title="Reference this headline"><i class="fa-solid fa-paragraph"></i></a></h1>
</section>
<section class="section" id="typo3-cms-system-notes-1">
<h1>TYPO3 CMS System Notes<a class="headerlink" href="#typo3-cms-system-notes-1" data-bs-toggle="modal" data-bs-target="#linkReferenceModal"  title="Reference this headline"><i class="fa-solid fa-paragraph"></i></a></h1>
</section>

I wonder if we could be less strict here and also parse an anchor properly even if it's missing the extra whitespace? That would make RST files a bit lina, I mean, leaner.