#6945: add a props block to sync mentions to wp.org

[gaambo]

Adds a "props" block as mentioned in #6945.

How

• Adds a new block wporg/props which is based on the core paragraph block (and similar to the notice block already existing in this repo).
• Block supports are copied from the core paragraph as of Gutenberg version 15.1 which includes text align, colors, typograph and spacing controls
• On save_post it checks for existance of this block (also supports nested blocks) and parses all mentions in this props block.
• The props are then sent to WordPress.org via WordPressdotorg\Profiles\add_activity.
• Synced props are stored as post meta and on updating a post they are compared and only new props are synced.
• It supports multiple props blocks in a post and also props blocks nested in others (like groups).
• It supports all post types atm.
• I've added the classnames dependency since its used in gutenberg and it's my go-to. But wasn't added in this package until yet and I don't think the DependencyExtractionPlugin of core handles that package. If we want to avoid this package for the simple two lines in this block, I can remove that.

Questions:

• How can I test the add_activity call? Is there a test instance or a local instance I can get when running via wp-env?
• Which values does the type parameter of add_activity allow?
• I'm assuming existing Make blogs use bbPress and therefore bbp_find_mentions to parse mentions. I'm reusing this function and provide a fallback if this is not available. If bbPress and this function will always be available, we can remove the fallback.
• It does not handle removing props (because I don't know if there's a remove_activity function?
• I'm using the generic save_post hook here but if we only want to support the post post type, I can switch that to save_post_post.

How to test:

1. Checkout this PR and run npm start + npm run wp-env start
2. Create a new post
3. Check the "Props" block is available in the inserter
4. Enter some text in the block like "Props to @xy"
5. You can add multiple props blocks and also nest them in others (like a group)
6. Save the post
7. ‼️ Atm this will trigger an error because on local environments WordPressdotorg\Profiles\add_activity does not exist
8. You can comment out this code, click update again and check that the meta field _wporg_props does exist and has the correct values in it

Screenshots:

[gaambo]

I've used npm run lint:js locally but don't get the error messages that the CI shows me.
Also I didn't commit my package-lock.json but classnames is in package.json so the CI build should get that?

[StevenDufresne]

This PR is closed. Is that correct? I'm under the impression that it should still be open.

[StevenDufresne]

I would avoid importing classnames. It don't think we need it for the block.

[gaambo]

This PR is closed. Is that correct? I'm under the impression that it should still be open.

@StevenDufresne
I didn't get any feedback or information if that block is still needed, or if I took the right direction. Also since the last commit the block API has changed and probably a few changes to the block should be made to work perfectly with the newest core versions. Since I had no time (and currently have no time) to work on this, I closed it.
Feel free to take it as-is and build on top of it.

[StevenDufresne]

👍 Okay. I've added this to my list of things :)