Issue #3071143 by KarimB, samsylve, smustgrave, quietone: Table Render Array...

 *   providing responsive tables.  Defaults to TRUE.

 * - #sticky: Indicates whether to add the drupal.tableheader library that makes

 *   table headers always visible at the top of the page. Defaults to FALSE.

 * - #footer: Table footer rows, in the same format as the #rows property.

 * - #caption: A localized string for the <caption> tag.

 *

 * Usage example:

 * Usage example 1: A simple form with an additional information table which

 * doesn't include any other form field.

 * @code

 * $form['contacts'] = array(

 * // Table header.

 * $header = [

 *   'name' => $this->t('Name'),

 *   'age' => $this->t('Age'),

 *   'email' => $this->t('Email'),

 * ];

 *

 * // Default data rows (these can be fetched from the database or any other

 * // source).

 * $default_rows = [

 *   ['name' => 'John', 'age' => 28, 'email' => 'john@example.com'],

 *   ['name' => 'Jane', 'age' => 25, 'email' => 'jane@example.com'],

 * ];

 *

 * // Prepare rows for the table element. We just display the information with

 * // #markup.

 * $rows = [];

 * foreach ($default_rows as $default_row) {

 *   $rows[] = [

 *     'name' => ['data' => ['#markup' => $default_row['name']]],

 *     'age' => ['data' => ['#markup' => $default_row['age']]],

 *     'email' => ['data' => ['#markup' => $default_row['email']]],

 *   ];

 * }

 *

 * // Now set the table element.

 * $form['information'] = [

 *   '#type' => 'table',

 *   '#header' => $header,

 *   '#rows' => $rows,  // Add the prepared rows here.

 *   '#empty' => $this->t('No entries available.'),

 * ];

 * @endcode

 *

 * Usage example 2: A table of form fields without the #rows property defined.

 * @code

 * // Set the contact element as a table render element with no #rows property.

 * // Next add five rows as sub-elements (or children) that will populate

 * // automatically the #rows property in preRenderTable().

 * $form['contacts'] = [

 *   '#type' => 'table',

 *   '#caption' => $this->t('Sample Table'),

 *   '#header' => array($this->t('Name'), $this->t('Phone')),

 * );

 *   '#header' => [$this->t('Name'), $this->t('Phone')],

 *   '#rows' => [],

 *   '#empty' => $this->t('No entries available.'),

 * ];

 *

 * // Add arbitrarily four rows to the table. Each row contains two fields

 * // (name and phone). The preRenderTable() method will add each sub-element

 * // (or children) of the table element to the #rows property.

 * for ($i = 1; $i <= 4; $i++) {

 *   $form['contacts'][$i]['#attributes'] = array('class' => array('foo', 'baz'));

 *   $form['contacts'][$i]['name'] = array(

 *    // Add foo and baz classes for each row.

 *   $form['contacts'][$i]['#attributes'] = ['class' => ['foo', 'baz']];

 *

 *   // Set the first column.

 *   $form['contacts'][$i]['name'] = [

 *     '#type' => 'textfield',

 *     '#title' => $this->t('Name'),

 *     '#title_display' => 'invisible',

 *   );

 *   ];

 *

 *   $form['contacts'][$i]['phone'] = array(

 *    // Set the second column.

 *   $form['contacts'][$i]['phone'] = [

 *     '#type' => 'tel',

 *     '#title' => $this->t('Phone'),

 *     '#title_display' => 'invisible',

 *   );

 *   ];

 * }

 *

 * $form['contacts'][]['colspan_example'] = array(

 * // Add the fifth row as a colspan of two columns.

 * $form['contacts'][]['colspan_example'] = [

 *   '#plain_text' => 'Colspan Example',

 *   '#wrapper_attributes' => array('colspan' => 2, 'class' => array('foo', 'bar')),

 * );

 *   '#wrapper_attributes' => ['colspan' => 2, 'class' => ['foo', 'bar']],

 * ];

 * @endcode

 * @see \Drupal\Core\Render\Element\Tableselect

 *