Post formats: Make title and description human readable

[carolinan]

What?

Closes #65319

This PR adds a new 6.8 compatibility file with a filter that makes the title and description of the post format templates human readable.
This change is already merged into WordPress 6.8 in https://core.trac.wordpress.org/ticket/62326
No additional PHP backport from Gutenberg to core is needed.

Why?

In the template data views, the post format templates showed the slug instead of a title, and there was no description.

How?

Filters default_template_types to add a description and title to the different post format templates.

Testing Instructions

First, you need a block theme, and you need to enable post format support on the active theme.

Example:

function twentytwentyfour_setup(){
	add_theme_support( 'post-formats', array( 'standard', 'aside', 'gallery', 'audio', 'video', 'link', 'image', 'chat', 'status', 'quote' ) );
}

add_action( 'after_setup_theme', 'twentytwentyfour_setup' );

Next, add a post format archive template inside the templates folder.
The content of the file does not matter for this test. I have used the link post format as example:
templates/taxonomy-post_format-post-format-link.html

Go to Appearance > Editor > Templates.
Note that the link archive is available, and that there is a name and description.

Screenshots or screencast

After: The link post format template on the Site Editor Template screen has a readable name and description.

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Co-authored-by: carolinan <[email protected]>
Co-authored-by: t-hamano <[email protected]>
Co-authored-by: Mamaduka <[email protected]>

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[t-hamano]

LGTM!

[Mamaduka]

Thanks, @carolinan!