Add gutenberg_get_remote_theme_patterns function

[oandregal]

Part of #45171

What?

Adds a new public function, gutenberg_get_remote_theme_patterns to query the patterns datum from theme.json.

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 gutenberg_get_remote_theme_patterns.
• Uses the new function in place of the call to the private class WP_Theme_JSON_Resolver_Gutenberg.

Testing Instructions

• Use any theme with theme.json and add the following:

{
  "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.

[oandregal]

I'm struggling to use the feature as per the testing instructions in trunk (also in this PR). I'll update when I know more.

[ntsekouras]

Looks good, thank you!

[ntsekouras]

I'm struggling to use the feature as per the testing instructions in trunk (also in this PR). I'll update when I know more.

Your instructions are good, but you have to ensure that the theme you're using allows remote patterns based on should_load_remote_block_patterns filter's value.

[oandregal]

ok, updated the test instructions with a different pattern/text search and it works perfectly (both trunk and this branch). Tested empty and twentytwentythree themes.

[oandregal]

Backporting at WordPress/wordpress-develop#4543