feat: TPC with late binding

[bshaffer]

Adds support for TPC by determining the API endpoint using the new SERVICE_ADDRESS_TEMPLATE constant in GAPIC clients and the "universe domain" from the auth credentials.

Requirements

• depends on feat: add support for universe domain (phase 1) google-auth-library-php#477
• depends on feat: late binding for transport later #491
• depends on feat: add support for Universe Domain via service address template gapic-generator-php#658

NOTE: It may be better to abstract some of this out so that the Handwritten clients can take advantage as well. For instance, in an ApiEndpointFactory.

[bshaffer]

Late Binding is no longer required, will close this and submit one without it.