Try 2: Add get and post/pages abilities.

[jorgefilipecosta]

Part of: WordPress/ai#40

Alternative to #10665, trying to implement what was discussed with
@JasonTheAdams and @justlevine.

This PR adds get abilities for post types via the Abilities API, enabling AI agents to retrieve posts and pages through core/post-type/{slug}/get. It Introduce a show_in_abilities option on register_post_type() to control which post types expose abilities, enabled by default for post and page for now (if we agree in this approach we will expand to menus, media etc)-
Support single-post retrieval by ID and multi-post querying with filters for status, author, search, taxonomy, meta, date, comment status, ping status and more.

I think the biggest decision we need to do is the naming of the ability. I went for core/post-type/{post-type-slug}/get where post-type-slug is the post type identifier (post, page etc). We could discuss other naming possibilities.

Test plan

Retrieve a single post by ID with meta and taxonomies (use a valid id):

await wp.apiFetch({
  path: wp.url.addQueryArgs(
    '/wp-abilities/v1/abilities/core/post-type/post/get/run',
    { input: { id: 334, include: { meta: true, taxonomies: true } } }
  )
});

Query posts filtered by meta key existence:

await wp.apiFetch({
  path: wp.url.addQueryArgs(
    '/wp-abilities/v1/abilities/core/post-type/post/get/run',
    {
      input: {
        include: { meta: true },
        query: {
          meta: {
            queries: [{ key: 'footnotes', compare: 'EXISTS' }]
          }
        }
      }
    }
  )
});

Nested meta query with AND/OR relations:

await wp.apiFetch({
  path: wp.url.addQueryArgs(
    '/wp-abilities/v1/abilities/core/post-type/post/get/run',
    {
      input: {
        include: { meta: true },
        query: {
          meta: {
            relation: 'AND',
            queries: [
              { key: 'a', compare: '=', value: '23' },
              {
                relation: 'OR',
                queries: [
                  { key: 'b', compare: '=', value: '1' },
                  { key: 'c', compare: '=', value: '1' }
                ]
              }
            ]
          }
        }
      }
    }
  )
});

Nested taxonomy query with AND/OR relations:

await wp.apiFetch({
  path: wp.url.addQueryArgs(
    '/wp-abilities/v1/abilities/core/post-type/post/get/run',
    {
      input: {
        include: { meta: true },
        query: {
          tax: {
            relation: 'AND',
            queries: [
              { taxonomy: 'post_tag', field: 'slug', terms: ['t-23'] },
              {
                relation: 'OR',
                queries: [
                  { taxonomy: 'post_tag', field: 'slug', terms: ['c-1'] },
                  { taxonomy: 'post_tag', field: 'slug', terms: ['b-1'] }
                ]
              }
            ]
          }
        }
      }
    }
  )
});

Retrieve most recent pages:

await wp.apiFetch({
  path: wp.url.addQueryArgs(
    '/wp-abilities/v1/abilities/core/post-type/post/get/run',
    { input: { id: 334, include: { meta: true, taxonomies: true } } }
  )
});

[github-actions]

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Props jorgefilipecosta, mukesh27.

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[github-actions]

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Test this pull request with WordPress Playground.

[mukeshpanchal27]

Quick review

[jorgefilipecosta]

This change is extracted in a different PR, and is a temporary just for testing.