Adjust post update hooks and allow custom fields in views

Problem/Motivation

When saving the view, we see the following error:

Deprecated function: mb_strtolower(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\Core\Config\Entity\Query\Condition->compile() (line 39 of core/lib/Drupal/Core/Config/Entity/Query/Condition.php).

This is because the UUID for the configured view is empty.

Also the new data_table property was preventing custom fields from appearing as options in section template views.

Steps to reproduce

Edit the section library view and save.

Create a new field on section templates. That field does not appear as an option to insert into the section library view.

Proposed resolution

Originally the new field UI was going to have the section library view as the parent so it was important for it to exist. That is no longer the case, so this MR removes the portion of the update hook that overwrote the entire config for the section library view.

Additionally, the associated post update hook to set the field_ui_base_route and wasn't updated when the field UI was moved.

This MR adds conditional post-update hooks for folks who already updated to a dev version of the module. If someone is upgrading from the latest release, those post-update hooks will just return "No changes needed to section library view." and "No changes needed to section template entity." respectively.

Testing

Three scenarios to test:

• Installing section library with this MR on a fresh site that did not previously have section library. (No updates should run.)
• Updating a site that was running the 1.2.2 release of section library is updated straight to the dev version + this MR (4 post-update hooks run but two will have no impact and simply return "No changes needed to section library view." and "No changes needed to section template entity." respectively)
• Updating a site that updated to the latest 1.2.x dev branch and subsequently added this MR. (Should run the two new post-update hooks.)

In all cases, the section library view should be editable and not display an error on save. Custom fields added to the section template entity should appear as options in section template views.