Tests: Switch runkit environment tests with @requires notation.
Tests: Mark tests that require the xdebug extension.
Tests: Mark tests that require the http extension.
Tests: Mark tests that require the curl extension.
Tests: Mark tests that require the gettext extension.
Tests: Mark tests that require the intl extension.
Tests: Mark tests that require the mysqli extension.
Tests: Mark tests that require the sqlite3 extension.
Tests: Fix codestyle errors.