getSupportedGlobalNetworkCallingCodes() public method

Convenience method to get a list of what global network calling codes the library has metadata for.
 public function testGetSupportedGlobalNetworkCallingCodes()
 {
     $globalNetworkCallingCodes = $this->phoneUtil->getSupportedGlobalNetworkCallingCodes();
     $this->assertGreaterThan(0, count($globalNetworkCallingCodes));
     foreach ($globalNetworkCallingCodes as $callingCode) {
         $this->assertGreaterThan(0, $callingCode);
         $this->assertEquals(RegionCode::UN001, $this->phoneUtil->getRegionCodeForCountryCode($callingCode));
     }
 }