Added ability to set 'rows' property for wysiwyg elements.

Usage example:

```
<item name="config" xsi:type="array">
    <item name="formElement" xsi:type="string">wysiwyg</item>
    <item name="wysiwyg" xsi:type="boolean">true</item>
    <item name="rows" xsi:type="number">10</item>
</item>
```

app/code/Magento/Ui/Component/Form/Element/Wysiwyg.php

@@ -55,7 +55,7 @@ public function __construct(
             \Magento\Framework\Data\Form\Element\Editor::class,
             [
                 'force_load' => true,
-                'rows' => 20,
+                'rows' => isset($config['rows']) ? $config['rows'] : 20,
                 'name' => $data['name'],
                 'config' => $wysiwygConfig->getConfig($wysiwygConfigData),
                 'wysiwyg' => isset($config['wysiwyg']) ? $config['wysiwyg'] : null,