Blocks: Add support for variations in block.json` file

We integrated variations with block types and the corresponding REST API endpoint in #52688. It's a follow-up patch to add missing support to the `block.json` metadata file when using `register_block_type`.

Some fields for variations are translatable.Therefore, i18n schema was copied over from Gutenberg: https://github.com/WordPress/gutenberg/blob/trunk/packages/blocks/src/api/i18n-block.json. The accompanying implementation was adapted as `translate_settings_using_i18n_schema`.

Props: gwwar, swissspidy, schlessera, jorgefilipecosta.
Fixes #53238.



git-svn-id: https://develop.svn.wordpress.org/trunk@51599 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -4267,6 +4267,54 @@ function wp_check_jsonp_callback( $callback ) {
 	return 0 === $illegal_char_count;
 }
 
+/**
+ * Reads and decodes a JSON file.
+ *
+ * @since 5.9.0
+ *
+ * @param string $filename Path to the JSON file.
+ * @param array  $options  {
+ *     Optional. Options to be used with `json_decode()`.
+ *
+ *     @type bool associative Optional. When `true`, JSON objects will be returned as associative arrays.
+ *                            When `false`, JSON objects will be returned as objects.
+ * }
+ *
+ * @return mixed Returns the value encoded in JSON in appropriate PHP type.
+ *               `null` is returned if the file is not found, or its content can't be decoded.
+ */
+function wp_json_file_decode( $filename, $options = array() ) {
+	$result   = null;
+	$filename = wp_normalize_path( realpath( $filename ) );
+	if ( ! file_exists( $filename ) ) {
+		trigger_error(
+			sprintf(
+				/* translators: %s: Path to the JSON file. */
+				__( "File %s doesn't exist!" ),
+				$filename
+			)
+		);
+		return $result;
+	}
+
+	$options      = wp_parse_args( $options, array( 'associative' => false ) );
+	$decoded_file = json_decode( file_get_contents( $filename ), $options['associative'] );
+
+	if ( JSON_ERROR_NONE !== json_last_error() ) {
+		trigger_error(
+			sprintf(
+				/* translators: 1: Path to the JSON file, 2: Error message. */
+				__( 'Error when decoding a JSON file at path %1$s: %2$s' ),
+				$filename,
+				json_last_error_msg()
+			)
+		);
+		return $result;
+	}
+
+	return $decoded_file;
+}
+
 /**
  * Retrieve the WordPress home page URL.
  *