[PWA URL Handling] Update URL handling explainer w/ feedback suggestions.

[LuHuangMSFT]

• Changes all usage of "URI" to "URL"
• Changes "excludePaths" to "exclude_paths" to follow JSON casing rules
• Changes "comment" to "description". This is an optional but recommended field that aids readability of the pwa-site-association file instead of a normal JSON comment
• Add "allow_all_associations" optional field to the top level of the pwa-site-associations JSON object. This allow site owners to allow handling from any app.

Resolves #295, resolves #296, resolves #297.

[domenic]

Nice!

I don't think this is a proper resolution of #297. In particular the description field has no processing model, so it should not exist in a specification.

[LuHuangMSFT]

Nice!

I don't think this is a proper resolution of #297. In particular the description field has no processing model, so it should not exist in a specification.

Do you mean that it is not processed or used? I don't feel very strongly about this. I can remove description if it is a clear anti-pattern.

[LuHuangMSFT]

description can be an implementation detail instead of being in the explainer. Does that work?

[domenic]

How does your implementation intend to use description?

[LuHuangMSFT]

How does your implementation intend to use description?

It is only for human readers, similar to comment in apple-app-site-association.

[domenic]

If it is not going to impact implementations, then it is best removed from the spec.

[LuHuangMSFT]

Removed description.

[HowardWolosky]

I'm concerned about the addition of allow_all_associations, and I added an additional comment to #301 to try and discuss that aspect further. You may want to consider removing that specific change from this PR and then merging it out since the rest of it looks good, and then tackle #301 in a separate PR once the discussion there resolves itself.

[LuHuangMSFT]

Removed "allow_all_associations" field from this PR to allow more discussion on #301.

[LuHuangMSFT]

As the current changes in this PR are almost entirely URI->URL and JSON formatting changes, and because we would like to migrate this explainer to a WICG repo as soon as possible, I will complete this PR and close the 3 related issues. If the issues should not be resolved, please reopen them in the WICG repo. Thanks.