Put the minimal code in place to support BP Block only Themes

[imath]

To progress about our ​BP Block Theme project, let's put in place some block template location code as well as a bp/content & a bp/title blocks.

You can try this code with ​BuddyVibes. It won't display much yet, but you'll see that if the Block Theme contains a buddypress.html template or in case of the Activity directory a buddypress/activity/index.html template, these will be loaded for all but Activity directory BuddyPress pages for the first and for the Activity directory page for the second.

Trac ticket: ​https://buddypress.trac.wordpress.org/ticket/8900

[imath]

Let's carry on working on this for next major release!

[imath]

In 13686:

Initialize the support of BP block only Themes

We are now using the locate_block_template() function to get block templates of BuddyPress content when active theme is supporting buddypress and is only using blocks.

For an example of this new kind of BP Themes, you can check the WIP we've started here: ​https://github.com/buddypress/buddyvibes

Here's a nice way to start 2024! Happy new year to everyone 🥂

Fixes #8900
Closes ​https://github.com/buddypress/buddypress/pull/104

M src/bp-core/bp-core-actions.php
M src/bp-core/bp-core-catchuri.php
M src/bp-core/bp-core-template-loader.php
M src/bp-core/bp-core-theme-compatibility.php