feat: implement GCE residency detection on Windows

[bshaffer]

See #469

Implement detection of Windows machines as a fallback when the metadata server ping fails. This is already implemented for Linux, but is currently bypassed for Windows.

google-auth-library-php/src/Credentials/GCECredentials.php

Lines 380 to 383 in 23e8e69

	if (PHP_OS === 'Windows') {
	// @TODO: implement GCE residency detection on Windows
	return false;
	}

Implementation details can be found at go/auth-library-noping, or by discussing with @TimurSadykov or @sai-sunder-s