THRIFT-5829 - Update TConstant.php to remove deprecated PHP code

[pierrestudios]

remove deprecated use of static callables

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[Jens-G]

1. Test\Thrift\Integration\Lib\ClassLoader\ThriftClassLoaderTest::testRegisterDefinition with data set "loadType" (array('/home/runner/work/thrift/thri.../phpcm'), 'Classmap\ThriftTest\Xtruct')
   ParseError: syntax error, unexpected '::' (T_PAAMAYIM_NEKUDOTAYIM), expecting ')'

/home/runner/work/thrift/thrift/lib/php/lib/Type/TConstant.php:44
/home/runner/work/thrift/thrift/lib/php/test/Resources/packages/phpcm/Classmap/ThriftTest/Types.php:4205
/home/runner/work/thrift/thrift/lib/php/lib/ClassLoader/ThriftClassLoader.php:109
/home/runner/work/thrift/thrift/lib/php/test/Integration/Lib/ClassLoader/ThriftClassLoaderTest.php:62

[Jens-G]

There's something boken here and should be fixed

[sveneld]

I will look on this week.

[pierrestudios]

I fixed the update in TConstant.php to make compatible wih PHP 7