Allow localhost for testing and development.

[rsolomakhin]

For testing and development, allow the (1) payment method identifier, (2) default application URL, and (2) supported origin to be localhost. For example:

• http://localhost:8080/some-path
• http://127.0.0.1:8080/some-path
• http://[::1]/some-path

Also update the deprecated RFC5988 with its replacement RFC8288, according to bikeshed's error message.

[rsolomakhin]

@domenic please take a look.

[domenic]

I don't think allowing such things at the spec level is the proper way to do things. Probably instead we want to have a developer tools' toggle that goes into a spec-incompliant mode. It'd be quite bad if someone deployed something on the internet that caused browsers to go look up and use payment method manifests on every visitor's machine!

[rsolomakhin]

Can you tell me more about the developer tools toggles? I'm not familiar with these.

[domenic]

Well, so for example, in Chrome's developer tools people have implemented a "Pretend you're offline" switch, or a "Disable cache" switch. We could add similar switches to Chrome if we wanted.

[rsolomakhin]

OK, let's go roll in this direction.