Scope extensions explainer: Avoid adding web to names

[kenchris]

Though the spec is called Web App Manifest, the web generally doesn't add "web" in API names, like currently used in the explainer, both as "web_apps" key and in the file name "web-app-origin-association.json".

We have even tried to avoid "app" when doable, but it seems that now the "id" proposal might even end up adding "app_id" key as Marcos' suggestion.

Maybe we could just call the file for "origin-association.json"? or "originlinks.json" which is similar to assetlinks.json. Anyway, the shorter the name, the more change that people will get the name right, I assume.

"web_apps" also doesn't say much, maybe something like "extensions" instead, or "allowed_extensions"

[kenchris]

or maybe "scope_inclusions" instead