Update class-wc-meta-box-coupon-data.php

Introduce `woocommerce_coupon_data_panels` action.

If someone wants to add a new tab to the Coupons data meta box, they can use the `woocommerce_coupon_data_tabs` filter to register a new tab. These tabs accept a `target` key that lets you specify the `div` ID to reveal when the tab is clicked on. It turns out, however, that there is no way to actually add the `div` to the page, making the filter for custom tabs only good for removing tabs.
fixed some coding standards in includes/class-wc-ajax.php
Made wc_get_product_terms support custom menu_order by using get_terms and an include

Fixes #5455
Merge pull request #5466 from claudiosmweb/improve-ajax-class

Fix some coding standards in includes/class-wc-ajax.php
Merge pull request #5458 from pippinsplugins/master

Update class-wc-meta-box-coupon-data.php
Add a tip for default selections, and use opt groups for the long bulk edit list