Fix for #7592

Added sku filter to the /products endpoint. 

Will let you search for products by sku without using the
/products/sku/<sku> endpoint. Its now possible to search for product
skus with specialchars like / and -.

includes/api/class-wc-api-products.php

@@ -520,6 +520,18 @@ class WC_API_Products extends WC_API_Resource {
 			$query_args['product_cat'] = $args['category'];
 		}
 		
+		// filter by specific sku
+		if( ! empty( $args['sku'] ) ) {
+		    if(!is_array($query_args['meta_query']))    {
+		        $query_args['meta_query'] = array();
+		    }
+		    $query_args['meta_query'][] = array(
+		        'key'     => '_sku',
+		        'value'   => $args['sku'],
+		        'compare' => "="
+		    );
+		}
+
 		$query_args = $this->merge_query_args( $query_args, $args );
 
 		return new WP_Query( $query_args );