ext/pdo: Size PDO::FETCH_BOTH rows for both keys of each column

UPGRADING

@@ -180,6 +180,10 @@ PHP 8.7 UPGRADE NOTES
 - MBString:
   . Improved performance of mb_strlen for UTF-8 strings.
 
+- PDO:
+  . Improved performance of fetching rows with PDO::FETCH_BOTH, the default
+    fetch mode, for results with more than 4 columns.
+
 - PDO_PGSQL:
   . Improved performance of the SQL parser that handles placeholders in
     PDO::prepare() and, with emulated prepares, PDOStatement::execute().

ext/pdo/pdo_stmt.c

@@ -735,7 +735,8 @@ static bool do_fetch(pdo_stmt_t *stmt, zval *return_value, enum pdo_fetch_type h
 		case PDO_FETCH_NUM:
 		case PDO_FETCH_NAMED:
 			if (!group_key) {
-				array_init_size(return_value, stmt->column_count);
+				/* PDO::FETCH_BOTH stores every value under its name and its index */
+				array_init_size(return_value, how == PDO_FETCH_BOTH ? 2 * stmt->column_count : stmt->column_count);
 			} else {
 				array_init(return_value);
 			}