Support Customize Menus

[valendesigns]

Fixes #2

[valendesigns]

@miina & @westonruter I'm thinking we may need to handle the transition to publish in this PR before it's ready for merge. Thought?

[westonruter]

@valendesigns transition to publish in what way?

[westonruter]

I think we can avoid duplicating the WP_Customize_Nav_Menu_Item_Setting::value_as_wp_post_nav_menu_item() method here by doing:

$setting_id = sprintf( 'nav_menu_item[%d]', static::MENU_ID );
$nav_menu_item = new WP_Customize_Nav_Menu_Item_Setting( $this->customize_manager, $setting_id, array(
    value: array( /* ... */ )
) );
$menu_items[] = $nav_menu_item-> value_as_wp_post_nav_menu_item();

[westonruter]

@valendesigns @miina I believe this will reduce the overall amount of code and re-use what is in WP_Customzie_Nav_Menus already: #56

With those changes merged into this PR, the resulting diff is much smaller: develop...bugfix/saving-menus-issue_3

I tried creating a new nav menu, assigning it to a nav menu location, and adding new nav menu items to it. I created the snapshot and loaded it on the frontend in both an authenticated and incognito window, and the snapshotted menu and nav menu items appeared as expected for me in both cases.

Please review.

[coveralls]

Coverage decreased (-1.6%) to 91.031% when pulling 310b365 on bugfix/saving-menus-issue_2 into cb45595 on develop.

[coveralls]

Coverage decreased (-1.6%) to 91.031% when pulling 310b365 on bugfix/saving-menus-issue_2 into cb45595 on develop.

[westonruter]

I think this is finally ready! 😂

[coveralls]

Coverage decreased (-0.6%) to 92.105% when pulling d5e0bbc on bugfix/saving-menus-issue_2 into cb45595 on develop.