Successor to PR #3523. There are 494 single-line changes (`public function provider` to `public static function provider`) in this PR. None of these were made manually; they were all created with the following script (adapted from
https://stackoverflow.com/questions/25909820/how-to-recursively-iterate-through-files-in-php):
```php
$dir = 'C:/git/unit10prep2/tests/PhpSpreadsheetTests';
$it = new RecursiveDirectoryIterator($dir);
// Loop through files
foreach(new RecursiveIteratorIterator($it) as $file) {
if ($file->getExtension() === 'php') {
$contents = file_get_contents($file);
$new = preg_replace('/public function (\\w*)([Pp])rovider/', 'public static function $1$2rovider', $contents);
if ($new !== $contents) {
echo "changing $file\n";
file_put_contents($file, $new);
}
}
}
```
After this PR, there will be one more, with a small number of test changes, and enabling PhpUnit 10 for Php 8.1+.
Fix#2810. Repairing some Phpstan diagnostics, used `?:` rather than `??` in a few places.
2 different Html modules are affected. Also, Ods Reader, but its problem is with sheet title rather than cell contents. And, as it turns out, Ods Reader was already not handling sheets with a title of `0` correctly - it made a truthy test before setting sheet title. That is now changed to truthy or numeric. Other readers are not susceptible to this problem. Tests are added.
oleibman
Adrien Crivelli