Fix attribute order in get_attribute_names_with_prefix()

- Follow same order as get_updated_html(): existing attributes first, then new ones
- Process all lexical_updates in HTML order (sorted by start position)
- Properly handle removed attributes, new attributes, and modified existing ones
- Use array_values(array_unique()) to avoid duplicates
- Passes 3 failing unit tests for order consistency
- Maintains PHPCS compliance

Fixes #64567

Author: whaze

src/wp-includes/html-api/class-wp-html-tag-processor.php

@@ -2853,23 +2853,10 @@ public function get_attribute_names_with_prefix( $prefix ): ?array {
 
 		$result = array();
 
-		// First, add existing attributes that haven't been removed
+		// First, add all existing attributes that match the prefix
 		foreach ( array_keys( $this->attributes ) as $attr_name ) {
 			if ( str_starts_with( $attr_name, $comparable ) ) {
-				// Check if this attribute is being removed in lexical_updates
-				$is_removed = false;
-				foreach ( $this->lexical_updates as $remove_name => $remove_update ) {
-					if ( ! is_int( $remove_name ) &&
-						$remove_name === $attr_name &&
-						'' === $remove_update->text ) {
-						$is_removed = true;
-						break;
-					}
-				}
-
-				if ( ! $is_removed ) {
-					$result[] = $attr_name;
-				}
+				$result[] = $attr_name;
 			}
 		}