Templates: allow replacing theme templates with custom templates

[liviopv]

What problem does this address?

The template replacing/swapping option only works with templates bundled in the theme. User might want to design their own templates and use them to replace theme defaults using the options shipped in recent GB versions and WordPress 6.5

What is your proposed solution?

The "Transform Into:" option available in the inspector sidebar for Templates should surface custom templates.

[annezazu]

Ah ha. Just ran into this with template parts and I assume it's the same problem. +1 to this cc @scruffian

[carolinan]

I am not able to reproduce this, perhaps more information is needed.

1. I created a new custom template through the Site Editor > Templates new.
2. I created a new page and clicked on Template, and chose "Swap template". My custom template is available.

I am not sure what "Transform into" is. I do not see it in the interface.

If you meant the following flow:

1. Activate Twenty Twenty-Four
2. Go to Site Editor > Templates.
3. Select and open the Blog Home template
4. In the inspector, open the panel labeled "Design".
5. View the optional designs.

If you meant that your custom template does not show under design, then these are not true theme templates, they are block patterns.