Description:
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Empty text nodes are supposed to be removed by DOMNode::normalize():
* PHP documentation: "Remove empty text nodes" https://www.php.net/manual/en/domnode.normalize.php
* DOM level 2 spec: "There are neither adjacent Text nodes nor empty Text nodes." https://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-normalize
* Latest WHATWG DOM spec: "If length is zero, then remove node and continue with the next exclusive Text node, if any." https://dom.spec.whatwg.org/#dom-node-normalize

The PHP implementation appears to combine adjacent Text nodes, but does not remove zero-length text nodes.

Test script:
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<?php
$doc = \DOMDocument::loadHTML('<p id=x>foo</p>');
$p = $doc->getElementById('x');
$p->childNodes[0]->textContent = '';
$p->normalize();
# This should print 0.  But it prints 1.
var_dump($p->childNodes->length);


Expected result:
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int(0)

Actual result:
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int(1)