[webauthn] update RP ID definition to allow for full URL syntax (#1406)

equalsJeffH has just created a new issue for https://github.com/w3c/webauthn:

== update RP ID definition to allow for full URL syntax ==
various web-enabled online services, such as SSH-in-the-browser are enabled using browser extensions (as one example) and do not have a classic domain-name-based host name, the latter being a (slightly loose) definition of an RP ID.

Given that the current RP ID definition is a proper subset of a URL (which is a subset of a URI), we ought to alter the WebAuthn spec's RP ID definition in order to officially accomodate these additional types of webauthn-wielding entities.

Please view or discuss this issue at https://github.com/w3c/webauthn/issues/1406 using your GitHub account