writeHTML(): whitespace around table cell content breaks text-align (7.x regression)

[naumso]

Environment: tecnickcom/tcpdf 7.0.6, tc-lib-pdf 8.70.3, PHP 8.5

In TCPDF 7, whitespace-only text nodes at <td>/<th> boundaries (and after
<br>) disable the cell's text-align. The same markup written on a single
line renders correctly. Per HTML whitespace-collapsing rules, inter-tag
newlines/indentation should not affect layout — and TCPDF 6 rendered both
variants identically. This hits any HTML produced by a template engine (Twig,
Blade, …), since generated markup is normally indented.

Reproduce:

$pdf = new TCPDF('P');
$pdf->setPrintHeader(false);
$pdf->setPrintFooter(false);
$pdf->setMargins(0, 0, 0, true);
$pdf->setAutoPageBreak(false, 0);
$pdf->setFont('freesans', '', 14);
$pdf->AddPage();

$css = '<style>.tbl { width: 205mm; text-align: center; }</style>';

// Variant A: single line -> centered (correct)
$a = $css . '<table class="tbl"><tr><td colspan="2">Centered text<br>second line</td></tr></table>';

// Variant B: same markup, indented -> renders LEFT-aligned (wrong)
$b = $css . '<table class="tbl">
    <tr>
      <td colspan="2">
        Centered text<br>
        second line
      </td>
    </tr>
  </table>';

$pdf->writeHTML($a, true);
$pdf->writeHTML($b, true);
$pdf->Output('repro.pdf', 'I');

Expected: both variants centered (TCPDF 6 behaviour).
Actual: variant B is left-aligned. Even a single space around the text node
(e.g. after collapsing all whitespace runs to one space) is enough to trigger it;
the alignment only survives when the whitespace touching the cell content is
stripped completely.

Workaround we use: pre-process the HTML with
preg_replace('#(<td[^>]*>)\s+#', '$1', …) / preg_replace('#\s+(</td>)#', '$1', …) /
preg_replace('#(<br\s*/?>)\s+#i', '$1', …) before writeHTML().