Avoid Service Worker update issues on localhost

[brandonpayton]

What problem is it solving?

This PR fixes #1180 - Playground on localhost sometimes fails to load due to failed service worker updates from "localhost".

How is the problem addressed?

By switching from "localhost" to the explicit loopback address "127.0.0.1". This avoids the case where "localhost" does not directly resolve to a loopback address.

For reference:
https://w3c.github.io/webappsec-secure-contexts/#localhost

Section 6.3 of [RFC6761] lays out the resolution of localhost. and names falling within .localhost. as special, and suggests that local resolvers SHOULD/MAY treat them specially. For better or worse, resolvers often ignore these suggestions, and will send localhost to the network for resolution in a number of circumstances.

Given that uncertainty, user agents MAY treat localhost names as having potentially trustworthy origins if and only if they also adhere to the localhost name resolution rules spelled out in [let-localhost-be-localhost] (which boil down to ensuring that localhost never resolves to a non-loopback address).

Testing Instructions

Run npm run dev and confirm the new dev server URL is http://127.0.0.1:5400/website-server/ and that local Playground loads successfully in your browser.

[brandonpayton]

Note: I do not know what remoteDevServerHost is used for, but since it seems to also be used by npm run dev, I went ahead and changed that to "127.0.0.1" as well.

[adamziel]

Good fix @brandonpayton!

Note: I do not know what remoteDevServerHost is used for, but since it seems to also be used by npm run dev, I went ahead and changed that to "127.0.0.1" as well.

It's used for remote.html URLs.

[adamziel]

@brandonpayton I ran into that issue again on 127.0.0.1 – could be related to a stale service worker or could be an actual problem. Nothing actionable yet. Let's keep an eye on this.

[brandonpayton]

@adamziel I ran into the same yesterday. I thought maybe it had something to do with a stale worker originally registered under "localhost". Unregistering the service worker and reloading the page fixed the issue, which seemed different than @mho22's experience here:
#1180 (comment)