Plugin settings page: Handle post type/template selection via REST/React

[johnwatkins0]

Feature description

Following up on #4998, which rebuilt the plugin settings screen using REST endpoints and components built for the setup wizard. One part that was largely left out of the updates due to its potential size and complexity was this:

Currently this is wrapped in the new settings page but handled the traditional way with settings saved on the backend via form submission.

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Acceptance criteria

• Options make sense in the context of the page
• Saving doesn't require a full page refresh

Implementation brief

• Details for for the various conditions will need to be ironed out
• Can probably use the AMP options endpoint.

QA testing instructions

Demo

Changelog entry

[johnwatkins0]

@westonruter Just confirming as I translate this bit into React, is this user_supported thing obsolete now?

<?php if ( ! empty( $option['user_supported'] ) ) : ?>
							<input type="hidden" name="<?php echo esc_attr( $element_name ); ?>" value="<?php echo esc_attr( $id ); ?>">
						<?php endif; ?>

[westonruter]

Correct! The user_supported is gone.

[westonruter]

I mean, it's just redundant now with supported.

[pierlon]

QA Passed

• Supported Templates options are correctly saved via a REST request
• The Templates section is hidden when Reader mode is chosen
• Toggling the "Pages" content type shows an alert and hides the Homepage template if all templates are not being served AMP