Add wp_get_remote_theme_patterns function

[oandregal]

Trac ticket https://core.trac.wordpress.org/ticket/58460
Part of WordPress/gutenberg#45171
Backports WordPress/gutenberg#49307

What?

Adds a new public function, wp_get_remote_theme_patterns to query the patterns datum from theme.json and substitutes current usage of private APIs.

Why?

We need to offer public APIs for consumers to add the data they need, so they don't resort to using private APIs.

How?

• Creates a new function called wp_get_remote_theme_patterns.
• Uses the new function in place of the call to the private class WP_Theme_JSON_Resolver.

Testing Instructions

• Use TwentyTwentyThree theme and add the following to its theme.json:

{
  "patterns": [ "partner-logos" ]
}

• Go to the post editor and open the inserter.
• Search for "logos".
• The expected result is that the pattern shows up in the list.

Also test that by removing the patterns from theme.json the pattern is not present.

Commit message

Themes: add wp_get_remote_theme_patterns function.

Adds a new public function, `wp_get_remote_theme_patterns` to query the `patterns` datum from `theme.json` and substitutes current usage of private APIs.

Props ntsekouras, poena, audrasjb.
Fixes #58460

[ntsekouras]

✅ Looks good, thank you!

[oandregal]

Deployed at https://core.trac.wordpress.org/changeset/55926

[oandregal]

Follow-up at #4640

[colorful-tones]

@oandregal I'm super curious as to what this PR is addressing. The testing notes and description leave me confused. I tried drilling through related Issues and Backport tickets, and I'm still lost.

Also, I had to Google "datum." 🤷‍♂️

I'm grateful for the work. Please explain in layperson's terms what use case or issue this PR solves.

[oandregal]

One of the fields of theme.json is patterns. So far, there wasn't any public API to get the value of that field. This PR introduces it.