MAGETWO-61209: Backport - Fixed issue #7379 with mage/calendar when setting `numberOfM…

[vasilii-b]

Description

The full description of the issue and steps to reproduce are provided in #7379.
The same issue is reproduced on Magento 2.1, Magento 2.2 and Magento 2.3-develop

Fixed Issues

1. Calendar widget (jQuery UI DatePicker) with numberOfMonths = 2 or more #7379: Calendar widget (jQuery UI DatePicker) with numberOfMonths = 2 or more

Manual testing scenarios

The easiest way to see the issue in action is to add a new field in the Magento_Contact form that is gonna use a calendar.

Field to add:

<div class="field availability">
  <label class="label" for="availability"><span><?= $block->escapeHtml(__('Availability')) ?></span></label>
   <div class="control">
       <input name="availability" id="availability" title="<?= $block->escapeHtmlAttr(__('Availability')) ?>"
            value="<?= $block->escapeHtmlAttr($this->helper('Magento\Contact\Helper\Data')->getPostValue('availability')) ?>" class="input-text" type="text" />
  </div>
</div>

Initialize the calendar:

<script>
    require(['jquery', 'mage/calendar'], function($, calendar) {
       $('#availability').calendar({
           numberOfMonths: [1, 2]
       });
    });
</script>

You should see only 2 months displayed, like this:

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

Original PR

#16279

[magento-engcom-team]

Hi @vasilii-b. Thank you for your contribution.
The changes from your Pull Request should be available with the upcoming 2.1.15 release.
Please check the release notes for final confirmation.