Fix: `partition_html()` fails parsing simple html (#2849)
Closes #2520.
Previously, `partition_html()` did not extract text from `<b>` tags
inside container tags (like `<div>`, `<pre>`). This PR provides support
for extracting text from `<b>` tags inside container tags.
### Testing
```
html_text = """
<!DOCTYPE html>
<html>
<head>
<title>A page</title>
</head>
<body>
<div>
<h1>Header 1</h1>
<p>Text </p>
<h2>Header 2</h2>
<pre><b>Param1</b> = Y<br><b>Param2</b> = 1<br><b>Param3</b> = 2<br><b>Param4</b> = A
<br><b>Param5</b> = A,B,C,D,E<br><b>Param6</b> = 7<br><b>Param7</b> = Five<br></pre>
</div>
</body>
</html>
"""
elements = partition_html(text=html_text)
print("\n\n".join([str(el) for el in elements]))
```
**Expected behavior**
```
Header 1
Text
Header 2
Param1 = Y
Param2 = 1
Param3 = 2
Param4 = A
Param5 = A,B,C,D,E
Param6 = 7
Param7 = Five
```
