Introduce Posts and Post Carousel block deprecations

[AnthonyLedesma]

Description

Closes #1632
Following the lead of the Gutenberg team, this PR introduces measures that will allow proper migration/deprecation from previously configured and published blocks into a working state using modern interface and features.

In this case, the core/latest-posts block had a number of breaking changes related to the implementation of a tokenized category selector. The new selector requires new logic and a new attribute schema.

This change is inspired by this PR in Gutenberg. This PR resolves a bug with migration from old-style coblocks/posts and coblocks/post-carousel attributes.

This can be replicated using old markup:

<!-- wp:coblocks/post-carousel {“columns”:3,“categories”:“1”} /-->
OR
<!-- wp:coblocks/post-carousel {"categories":"4"} /-->

<!-- wp:coblocks/posts {“className”:“is-style-stacked”,“categories”:“3”} /-->

Please note This fix will successfully migrate the chosen category from a previously configured block into a category token within the new interface. While the token exists and works as expected as a filter, the token is missing contextual language. This is a known issue with migration.

Types of changes

JavaScript changes and PHP changes.

How has this been tested?

Tested manually migrating from 5.4.2 -> 5.5
Tested with and without the Gutenberg plugin.
Tested migration from CoBlocks 1.23.0 -> 2.2.2

Checklist:

• My code is tested
• My code follows accessibility standards
• My code has proper inline documentation
• I've included any necessary tests
• I've included developer documentation
• I've added proper labels to this pull request

[cypress]

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Test summary

14 • 0 • 0 • 0

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Run details

Project	CoBlocks
Status	Passed
Commit	67f84b3
Started	Aug 21, 2020 3:49 PM
Ended	Aug 21, 2020 3:50 PM
Duration	01:42 💡
OS	Linux Debian - 10.4
Browser	Multiple

View run in Cypress Dashboard ➡️

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[jrtashjian]

This is great! On the issue with the blank token in the field, we can actually fix this during the attribute migration.

The functionality I'm seeing in the block using it new is the REST API response data is saved for each category in the attribute. Personally this seems way too verbose but maybe there is a reason. Regardless, we can perform an API request to get this additional data for the category ID's we find. Here's an example I've used in my own plugins:

import apiFetch from '@wordpress/api-fetch';
import { addQueryArgs } from '@wordpress/url';
import { decodeEntities } from '@wordpress/html-entities';

apiFetch( {
        path: addQueryArgs(
            '/wp/v2/categories',
            {
                per_page: 100, // should be set to the number of categories we are querying.
                _fields: 'id,name',
                include: categoryIDs.join( ',' ),
            }
        )
    } )
    .then(
        ( entities ) => entities.map(
            ( entity ) => (
                {
                    id: entity.id,
                    name: decodeEntities( entity.name ),
                }
            )
        )
    )

So this PR would migrate to this:

<!-- wp:coblocks/post-carousel {"columns":3,"categories":[{"id":3}]} /-->

but we need at least this:

<!-- wp:coblocks/post-carousel {"columns":3,"categories":[{"id":3,"name": "Category 2"}]} /-->