THRIFT-5082: Add a Class reference for PHP enum $_TSPEC

[spwin]

Issue described in the ticket: https://issues.apache.org/jira/browse/THRIFT-5082

This adds the class reference to PHP $_TSPEC

BEFORE

5 => array(
  'var' => 'group_type',
  'isRequired' => true,
  'type' => TType::I32,
  ),

AFTER

5 => array(
  'var' => 'group_type',
  'isRequired' => true,
  'type' => TType::I32,
  'class' => '\thrift\groups\GroupType',
  ),

[mmuszynskifln]

Nice!

[spwin]

bump

[dcelasun]

Thanks for the PR @spwin! Can you please add a test case so this won't regress in the future?