Improve WP Playground compatibility

[imath]

I've found various issues:

In BP Nouveau: Activity items action buttons are not styled the right way looks like the bp_current_component() is not set during the Ajax context.
In BP Legacy: a "Deleted" template error notice is always displayed.
this query SELECT object_id FROM wp_bp_xprofile_meta WHERE object_type = 'field' AND meta_key = 'signup_position' ORDER BY CONVERT(meta_value, SIGNED) ASC generates an error : General error: 1 no such column: SIGNED.
It's not possible to upload Avatars (error is Upload Failed! Error was: Please upload only these file types: JPG, JPEG, JPE, GIF, PNG, WEBP.) or cover images (error is Upload Failed! Error was: Specified file failed upload test.).
I need to investigate further.

As WP Playground is putting WordPress in a subdirectory I believe it’s problematic. When testing using wp-now npm package I don’t get most of these errors.

To fix WP Playground issues, I suggest to:

• Send the current canonical URL into Ajax request vars. wp_get_referer() is not set which explains why BP URI globals are not set into Ajax context by WP Playground.
• Ignore $_COOKIE['bp-message'] if its value is set to deleted. It looks like the cookie is not deleted but its value is set to deleted once it's removed by BuddyPress.
• About the SIGNED conversion or casting SQL issue, it looks like it's a SQLlite issue that will be hard to cope with: see ​https://wordpress.org/support/topic/wordpress-meta-query-not-working/ I used a workaround to get rid of it for now.

[!IMPORTANT]
I'll need to run grunt commit before SVN committing this PR.

Trac ticket: ​https://buddypress.trac.wordpress.org/ticket/9207

[imath]

Let's try to finally use WP Playground to let users preview BuddyPress from the plugin directory!

This will help us prove: BuddyPress is working with any supported WordPress versions. Visiting our ​Plugin Reviews motivated me about this move.

[imath]

In 14068:

Improve BuddyPress compatibility with WP Playground previews

• Avoid using SIGNED casting into the SQL query retrieving the signup field IDs as it's generating an error with WP Playground SQLite db.
• Make sure BP URI globals are set during Ajax requests passing the current displayed page canonical URL into these requests.
• Ignore the bp-message cookie when its value is set to deleted to prevent the wrong display of a template notice when BP Legacy is the active template pack.
• Update JSON blueprints to latest WP Playground's blueprint schema.

Props espellcaste

Fixes #9207
Closes ​https://github.com/buddypress/buddypress/pull/389