`get_text_content` will transform contiguous space chars into single
spaces, plus translate special HTML elements
```
>>> " ".join(html.fromstring(f"a\n b & c").text_content().split())
'a b & c'
```
In order the correctly verify if a term is text-only we need to use the
HTML parser. Note that to be resilient against bad XML, but valid HTML,
we cannot use the default XML parser.
Part-of: odoo/odoo#150152