Fix code style issues in EntityStatusTest and StemmerTest

Problem/Motivation

All method arguments with default values should be declared after the method arguments without default values. Otherwise, it makes it impossible for callers to take advantage of defaults; they must re-specify the defaulted values in order to "get to" the non-default arguments.

File: search_api/tests/src/Unit/Processor/EntityStatusTest.php

83: public function testSupportsIndex(array $datasource_ids = NULL, $expected) {

Proposed resolution

83: public function testSupportsIndex($expected, array $datasource_ids = NULL) {