HTML Reader does not handle br in table cells correctly

[make-all]

This is:

- [X] a bug report
- [ ] a feature request
- [X] **not** a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

The HTML Reader should produce a cell with two lines of text when parsing a table cell containing a br tag.

What is the current behavior?

The cell produced initially appears in Excel as a single line, although editing the cell results in the expected display.

What are the steps to reproduce?

Please provide a Minimal, Complete, and Verifiable example of code that exhibits the issue without relying on an external Excel file or a web server:

sample.html:

<table>
  <tr><td>First Line<br>Second Line</td></tr>
</table>

<?php

require __DIR__ . '/vendor/autoload.php';

// Import from html
$spreadsheet = \PhpOffice\PhpSpreadsheet\IOFactory::load('sample.html');

// Write the resulting spreadsheet as xlsx
$writer = new \PhpOffice\PhpSpreadsheet\Writer\Xlsx($spreadsheet);
$writer->save('sample.xlsx');

Which versions of PhpSpreadsheet and PHP are affected?

All versions up to at least 1.7.0, all versions of PHP

Proposed fix

The cell requires the wrapText attribute to be applied, as in pull request #1070